I've spent a great deal of time in Galloway (it was my back door as a kid for holidays and it still remains so). I was there (and visited High Auchenlarie) thrice over the summer and spent a week at Gatehouse last October. I've a number of photos of the cairn but there seemed to be absolutely no discernable circle there at all. A lot of high-level field clearance for sure but I saw no circle. Some "stone settings" which probably are cairn kerb remnants (mibbe) and field dyke remnants (probably) jumbled around the area of a robbed cairn (though admittedly a rather nice one). Some of parts of those "stone settings" form two semi- portions-of-an-arc, but their geometry does not seem to relate to one another.
There is also a "new" circle/ stone setting nearby (1/2 km away) whose construction involved some movement of C&R stones/ boulders. I shall say nothing more of this.
I am back down at Gatehouse soon (for a week in mid-October) and I know the short distance along the hill from Lagganmullan to Auchenlarie very well. Some lovely recently found C&R panels and boulders strewn across the hillside. Many others submerged under turf, like this one from June 2012.

http://www.themodernantiquarian.com/img_fullsize/108048.jpg

I'll take plenty of pics - but I'm with Canmore on this one. By the way Tiompan - if you are down that way it is worth your while politely popping by Kirkdale House for a polite gander at the rockery...