Quick follow up. The original problem still exists with the pitchbend settings, but I did find the solution to make this work with my ROLI.
If anyone else is having the same issue you want to have the Seaboard with (NoteExp) selected for your midi input, not the normal Seaboard you would select for other MPE instruments. Then set Channel Input to Any and Group and Channel to 1 and use the Note Expression window to assist with selecting which MPE elements are on. You can only do Slide, Glide and Pressure but it is enough to create some interesting changes to the patch in real time.
I’d still be curious if someone could report if they see the same problem with the pitchbend maxing at +24.