My own experience with a 4.5 90mm Nikkor on a Sinar P:
Bag bellows - essential, especially for big shifts, you just cant bend them that way without damaging them
Recessed lens board - I've only twice thought it'd be helpful, both times trying to focus major tilts but in stopping down the lens and using a hyperfocal infinity focus I got around the issue... The real solution would be that Sinar didn't make the P standard rail connection blocks or tripod thingies as large as they do, maybe not an issue with your camera
- maybe it is, hence the different opinions...
If anyone says their bellows works then either they have a super soft/short one (no good for portraiture on longer focal lengths) or their lens has poop coverage and/or they just aren't shifting enough to notice...