Sorry you have such bad luck with paphs. Mine actually get more light than the experts recommend, but they love it. They're very close to a window that I have tropical plants growing in, so the tropicals help diffuse the light to keep the paphs from having sun beating on them relentlessly, but they definitely do get some direct sun in the afternoon as it passes by that window. It's only for about half an hour or 45 minutes, but that little "boost" really seems to work well for them. I get foliage growing like gangbusters, and my Heron's Faire was just about to bloom for me a couple of weeks ago, but then we went on vacation and my hubby turned off the AC and the buds blasted. I nearly cried.
But anyway, if your paphs are under-performing, you could always move them closer to the window. What's the worst that could happen? A little leaf sunburn? They can recover from that. If you'd like to put them behind your oncids, try to position them so that they get some dappled sunlight. Mine are never in total shade all the time. I also fertilize mine regularly with a high-nitrogen fertilizer. I was told by a really good grower that they need lots of nitrogen to make all the foliage they need to support blooms. I do notice that if I forget the fert for a while, the growth slows significantly. So the high-nitrogen fert is a must for them, I'd say.
Anyway, I wish you lots of luck with the paphs. Don't give up! Who knows...maybe someday we'll be comparing pics of our Sanderianums!