With my FM1002 running a DVO Topaz T3, at first I thought that regressive dip in the end travel would be a big issue and added 3 positive volume spacers to the initial build. Then I dropped it to 2, then 1. Now I’m thinking about trying it with none.
The Topaz is already a bit more linear than most RS or Fox shocks and yet on most rides at a rider weight without gear of about 200lbs I barely use 70% travel. Even big (for me) jumps rarely pass 80 or 85%.
You may find that with air shocks, the regressive dip just isn’t a huge issue. I think a lot of us are overcompensating for it a bit with volume spacers.
As for shock tuning in general…you’re in luck, the FM1001/1002 and even 1003 all have kinematics that are pretty decent with standard aftermarket Medium tunes.
You could always have a pro tuner dial the shim stack for your weight and terrain, but if you’re getting a standard aftermarket 2023 Super Deluxe Ultimate with the new silent spring backed IFP damper, I’d just bolt it on and spend some time riding it first. You may not need damping changes all that urgently.
