As always you have to try it. But I would orient the main speakers on the short wall. you want your listening position to be an equilateral triangle with the left and right speakers for 2 channel listening. You want the two front channels away from the wall, and sidewalls. Having space behind your head is good to prevent rear wall reflections. Have a chair you can move into listening position if needed.
I helped a friend of mine put together a system in a similar sized room. He has done months of experimentation and finalized it on the short wall. The key is to put good absorption behind and in the corner of the speakers (you can experiment with couch cushions, pillows, tripled over blankets. Also, throwing a heavy blanket over the tv when listing to two channel will help imaging. Doesn’t mater much for HT.
Hope this helps.