I've asked Apex on how to mount plate long time ago. I was mostly asking about axle width and plate positioning for regular carving on 180cm board.
I've also asked to measure distance from tail to plate, to have reference for front-back positioning. I was also using 4x4 mount at a time. UPM mount only gives you 2-3 options.
Here's full quote:
From what I remember, there are three holes in the front and two in the back. Answer above pretty much rules out one hole on the back (use front only) and one hole in the front (rear, so use front or middle one).
I was mounting both mounts symmetrically (i.e. 1/5 position on front and rear) on both end.
The procedure was the the following:
1. Insert pins so they stick out to the side of plate.
2. Match rear ping with hole on the rear mount.
3. Match front pin in the beginning of slide. It will move forward when you turn.
4. Move all that construction so mounts are symmetrical around board inserts. Figure out what mount holes to use, and what holes on 4x4 mounts to use.
5. Mount em. Don't tighten yet.
6. Put plate normally, insert all four pins.
7. Push on top of the plate to make sure it slides.
8. Remove plate and pins and tighten everything.
9 Attach plate and bindings on top. Add spacers on the inside/outside if needed
I usually went through steps 6-8 to make sure everything is straight. May be it wasn't necessary, but it's better safe than sorry.