I wanted to send you special snaps for your reasoning here. Those little polar plugs are what should give anyone doing chicken fecals a little fright.
The subtle differences can be seen in the overall shape of the egg, but most importantly, in the size of the egg. The capillaria egg will be quite a bit larger than the monocystis. This is all well and good until you try to measure an egg under a microscope. It can be tricky, but often exact measurements are important to properly ID structures.
The good news is that some cameras do that automatically, which is something I super want because I am lazy. But as it is now, if you have a reticle (an eyepiece with a scale) you can use that to measure things. (you need to work out specifically what each mark on your reticle measures in mm, every microscope is different, but once you do that, it's relatively simple).