Chukars are awesome but they are also nasty nasty birds (tempermental)
I don't personally raise birds beyond pigeons for training but have been given some pearls of wisdom from guys that know. Your flight pen is good and feeding them on the platform seems to make sense.
Moulders Farm gave some very good advice that is consistent with the key to good birds as relayed to me from a fella who has fantastic Chukars. He keeps them in a 20 x 40'ish flight pen on wire. He has it located far away from his operation and away from daily activity. He told me the key in unison with that is to feed them only at night and deliberately avoid contact to the best of his ability. Can't say for sure that this is his entire recipe but what I can say is he consistently has very strong flying, healthy, and spooky Chukars so take it for what it's worth. If I get birds from him I do not have near the capacity he does so they are in a small cage awaiting you know what (poor friggin' birds). I've gotten lazy at times with a few leftovers and having kept them for 2-3 weeks..my laziness seems to rub off on them and then it's a crap shoot as to how well they will do while training - I try to avoid that.