The away section is closed off by a fence that, I don't think, can be moved. I'm guessing the allocated tickets is based on a % of that being filled as they can't spread out fans out in to other areas of the stand without giving us a whole other one to ourselves.
The issue of what percentage STs actually attend is interesting, and tied up in demographics, occupational opportunities and simple geography. A larger splodge of Dons supporters work in the central belt rather than vice-versa. Hence the good turn outs at ER and Tinyplace, and the lower percentage of their own turning up at Pityfulrodrie.