Yeah, I had the same problem with Cassiel.
After trying to force them in for about 10 minutes, and checking the information online again to make sure I'd ordered the right size eyes, I ended up slitting the eye pockets with a wirecutter
I didn't have that problem with the OTHER 1/6th Obitsu head I have... because I stripped the eye pockets out before installing the eyes. (Honestly, I think I prefer using eye putty to having the sockets.)
I have so many dolls that I can't fit all their names in my signature anymore. @__@