First part of your question (what other Trapshooters use for their POI):
You're going to get a hundred different answers all over the map from 50/50 to 120% high,
none of which will really be all that helpful in choosing your own best Trap-specific POI.
In fact, see the results of this poll:
POI Poll on trapshooters/com
[Note that well over half (58%) of respondents are in the 60/40 to 80/20 range, which is a pretty accurate poll in my experience, with an additional 12% at 90/10].
Second part of your question (lowering your POI):
I was thinking of moving to 90/10 as I sometimes miss straight aways bc I shoot a little high.
Additionally, if you're thinking of lowering your POI from 100% high to 90/10, why ask us? Just do it and see if your results improve. But note the following: if you're truly shooting completely over targets (but as you said, only "some" targets, not all), you're not missing them by the difference between 100/0 and 90/10 (which is only a few measly inches) . . . you're mispointing the gun by half your pattern's diameter, and maybe more. So, be honest with yourself: POI setting problem or a shooting skill/consistency problem?