Rumors are that you can't schedule a FP+ within 2 hours of an ADR, but that was not our experience. I've also seen rumors that if you are on the website you can schedule them in that time, but on the app you can't not. Don't know if that is true, but if you are trying on the app and can't do it, then it is worth a try on teh website.
We are all day park people, but we almost all ways have a TS sometime between 11:30 and 12:30, and we do want to ride Soarin, TSM etc. by FP before that. That was our pattern before FP+ and we don't really want to change it- especially at EPCOT where we usually go to WS at lunch and then stay over there the rest of the day.
I had no problem on the website scheduling FPs for 10:00 and 11:00 a.m. when I had ADRs in our usual time frame. It would even try to set them right through our ADR times and would pop up a warning that they were set in an ADR. Even though it had a warning, you could proceed and set them there though.
Good luck! Hope it works for you! Report back because I'm interested in whether you have issues. If you do, that creates yet another unworkable FP+ problem for my family.