The closing lines of the LRP, before the final QC, have been the cause of much debate and are the only part of the ritual that seems to have changed in the hands of different magicians over the years. Thus, today there are multiple variations of these lines, from the original "Before me flames the pentagram and behind me shines the six-rayed star" to the Crowley version of "For about me flames the pentagram and in the column shines the six-rayed star", and some slight variations of the two. All of them are perfectly valid, and there are justifications, usually in the form of gematria, for them all. This post will explore some of the variations and the reasoning behind them.
First there is the original format employed in both the GD and SM and printed in Regardie's The Golden Dawn: "Before me flames the pentagram, and behind me shines the six-rayed star". On the surface this does not make sense, for the pentagram is not "before" the magician, but rather there are four of them around the magician, including behind him or her, where the hexagram is stated to be. Regardie suggested the visualisation of a pentagram on the chest and a hexagram on the back, indicating that the pentagram here mentioned has no relation to the four already drawn. This refers to the microcosm (the human, represented by the pentagram [somewhat akin to the extended figure in Da Vinci's Vitruvian Man, with the five points of the body relating to the head, two arms, and two legs]) and the macrocosm (the "more than human", the divine man, the Adam Qadmon, represented by the hexagram, symbolic of Tiphareth, where the Higher Self dwells).
But there is no specific indication as to why the pentagram is before the magician and the hexagram behind, although the Ciceros give an interesting suggestion in footnote 20 on page 66 of their annotated edition of Regardie's The Middle Pillar: "The positioning of a hexagram behind the magician alludes to an advanced working in which the magician visualizes the Golden Dawn's Banner of the East within his aura." This does not personally make sense to me, as the magician would be facing East (where the Banner of the East is positioned) and stating "before me flames the pentagram", whereas the hexagram is linked to the Banner, not the pentagram. I would imagine the Banner of the West behind the magician, since the magician faces East at this point of the ritual, but all of this is speculation at present, as I'm not aware of exactly what the Ciceros were describing in this footnote.
The main alternative to the above is the one we get from Crowley: "For about me flames the pentagram and within the column shines the six-rayed star". This is the one that I and most others I encounter prefer, and I think for good reason, as there is more justification behind the use of the words. Firstly the "about me" relates to the very obvious fact that the four pentagrams just drawn are about or around the magician (some alternatives use "around me"). The column is the magician him or herself (symbolism lost in the alternative of "within me"), standing in the centre of the circle surrounded by the pentagrams. This column is an allusion to the Middle Pillar, and thus it subtly affirms a balanced disposition in the magician, who is symbolically identified with the Pillar of Balance. This adds an essential symbolic ingredient to this ritual which falls in line with all Golden Dawn teaching, to avoid the extremes of mercy or severity. Affirming this on a daily basis adds an extra layer to the ritual. Combined with this is the same symbolism of the macrocosm linked to the hexagram, only this time the hexagram is to be imagined within the column that the magician represents, centred around the heart region, which is the area of the body linked with Tiphareth, which, as the sixth Sephirah, is represented by the hexagram and again symbolises the Higher Self of the magician.
But what of the microcosm? This is still present in the ritual, in the pentagrams that are "about" the magician. To try to make this point clear, imagine the circle drawn around the pentagrams - this is the microcosm, the symbolic extension of the aura of the magician. Then imagine a smaller circle contained within this circle, representing the central pillar, where lies the hexagram, the macrocosm. This, therefore, intimates that the macrocosm is contained within the microcosm, just as the microcosm is contained within the macrocosm (the much larger circle of the universe around the personal circle or sphere of the magician). This "inner macrocosm" is the inner spark of Divine Light within each person (As Above, So Below) and this is affirmed in symbolic fashion with this variation of these lines in the LRP.
There is an interesting element to this variation which can be found via gematria. If we take the value of the four pentagrams (4X5=20) and add the value of the single hexagram (6) we get 26, which is the number of the Tetragrammaton, YHVH. Aside from the obvious relation to God, it could be seen as relating, via its four-fold nature, to the four directions, the four Pillars the four Archangels, and so forth, thus tying it further to the LRP, and the East in particular, where this God-name is utilised, and where the Light of the Dawn shines forth into the personal sphere and temple of the magician. But this is not all, for 26 is also the number of the Middle Pillar (Kether=1, Tiphareth=6, Yesod=9, Malkuth=10; 1+6+9+10=26), thus relating to the column mentioned in these lines and the symbolic invocation of Light down the Middle Pillar (and the magician's ascent back up).
There is a variation that suggests a hexagram should be drawn or imagined above and below the magician, thus "sealing" all six directions of the magician's sphere (front, back, left, right, up, and down). While this has merit (including a gematric link  to AHYHVH, the amalgamation of AHYH and YHVH, the God-names of West and East), there is no need for this, as the pentagrams can sufficiently seal the personal sphere of the magician, while still allowing the Light of Kether to enter. Besides, the hexagram is not intended here to banish or seal, but to represent the hidden macrocosm, the Higher Self, within the magician.
Finally there is an additional line present in an AO version of the LRP: "And above my head the Glory of God". This was probably added to differentiate it from the rebels in the Stella Matutina and is much more religious in tone (suitable for the prayer aspect of this ritual). In many ways, however, it is not necessary, and one could even argue that it intimates that God is only "above" as opposed to also being present within each of us, particularly as we invoke the Light during this ritual.