'Micro adjust' saddle clamp not allowing fine enough adjustment (on SP12 suspension seatpost)

I have an Suntour SP12 seatpost, and the saddle is held on by two clamps on either side. The clamps are splined, but these splines only allow adjustment of around 6-8 degrees which is far too much for me to find a comfortable position.

Red circle = side of seat post (with outwards facing splines)
Blue circle = inner side of clamp (with inwards facing splines)
Green circle = outer side of clamp

The outer side of clamp is not splined, it stays in position by wrapping around the saddle rail in combination with the inner clamp. Because this isn’t perfectly machined, there is some play that can be used to add maybe 1-2 degrees of adjustment (by putting weight on the rear or nose of the saddle while tightening). However, this still leaves 2-4 degrees of adjustment unavailable (and it feels a bit janky).

I tried swapping the inner clamps, in the hope that the splines were in slightly different positions, but it didn’t help. I have tried this morning to use a rubber washer between the seat post side and the inner clamp, but it wasn’t strong enough. However, I only used a piece of an old silicone phone case, and about 24nm of torque because I was worried of breaking something. Maybe this could work with a proper rubber washer? But I doubt it

Any ideas? I don’t mind making some kind of mount from a bit of metal bent around and screwed into the sides, but I don’t know to spline it to make it stay in position. Or maybe some old saddle rails, and a mount screwed onto those?

The suspension makes a lot of difference to me, so I would like to find a way to make this seatpost work. Although I suppose I could go for the thudbuster instead – it’s just quite expensive.