PhilDAS never content with the bikes I already own

I suspect this particular frame had an issue from the factory.

I got it on here as cracked and "repaired" the crack myself but didn't fix the issue which made the crack which is that the seatpost slips. It has a silly internal wedge clamp to hold the post in place and despite modifying the clamp so that it can press against the seatpost harder and the textured gritty finish on the seatpost I can't get it to stay put. Clamped up way above torque, I can whack the saddle with my hand and the post goes down a touch. Riding it, this means that the seatpost goes down by about a cm in 15 minutes or so.
I've tried a spacer behind the clamp so that it is further toward the seatpost and pushing more against the post but no better. It's covered in carbon assembly/grip paste, no good.

I've basically given up on the idea of getting the seatpost to stay put.
It is a very common issue with this frame but the solution for most is to just over tighten it which clearly an original owner has tried hence the cracking.

I paid for the whole bike basically the cost of the parts so the frame owes me nothing and therefore I'm not too concerned about ever selling it. I'm only concerned with adjustability in case I change shoes/pedals/saddle/crank length and it no longer fits perfect