I would imagine that depends on a number of factors. The impressions I take for acrylic customs are open mouth with a ~1" bite block and I don't have that problem but my ear canals are almost certainly different in size/shape to yours and probably deform differently when I eat/smile/talk. I know some audiologists recommend trying those things with your impressions before sending them off to make sure the final product will be comfortable but I've never done that.
I would give it a few days to see if you get used to it and if not maybe contact CTM to see what they have to say. You could also see if there's any info in the multi-custom thread or ask average_joe.