Say we've got (2) 2.4 APs 12 miles apart but seeing each other with a -65. All timing sensitive settings are the same and distance is set to 8 miles. Would these two APs still be synced and not interfere with each other or would I need to increase the distance setting in both APs to at least 12 miles achieve this?
The distance is irrelevant as long as it's the same setting on both sides. You might also want to add some down tilt on each side's sector if they're seeing each other at that power level.
Check out this white paper on frequency reuse... it's for ePMP, but the fundamentals apply to PMP450 as well. I looked around for a PMP450 white paper on frequency reuse, but couldn't find one... maybe someone from Cambium could point us in the right direction?