At a site we have 20Meter POE ethernet leads connecting AP's + PTP's and we have noticed that occasionally OSPF state changes can be high (20-60) over a 24 hour period, we have tried using different OSPF network type = Point to Point and Broadcast
Is there anything else we can do to reduce state changes?

First you need to find out the reason for state changes. Is it a link flap?

I would also pin this rather on an underlying ethernet issue. 20+ flaps in 24 hours is a lot.

Ethernet errors, packet loss? anything at all wrong with the links?