What he said ^^^
They will flex quite a bit, I do the same thing. Get the round part to fit how you like, then pull the lower part down tight to test the fit, sand and repeat. Keep doing it that way until it sits tight how you like it, then attach the top two screws and then the bottom. I have often had to drill a different hole to make it tighter, had to do this on the used CAP I picked up. The rubber neck trim hid the old open hole, so it was no problem.
As somebody else said, worse you can do is mess the ears up more and then order a set from ATA anyway, so no big deal, either way.