I tried using an Optimus Sig V2 removed from my Apex XII onto the Z690 Hero with 12900KS. Was not getting good contact with the IHS. Thought it was the lower 1700 IHS than the 1200, about 0.031 inch. However, Optimus tech said the 1200 mount hardware has enough range. What I was getting was poor contact at the top rear of the socket, like a tilt of the entire area. The board is quite warped in the area of the socket. This is not due to pressure from the closed ILM, but from the fab. I don't know about the other Maximus Z690 types or runs, but this one required post/washer adjustment to compensate, somewhere around 0.010 - 0.012 between opposite corners.
I recently have tried a der8auer Contact Frame and an HK IV Pro with solid 1700 Backplate and gained about four more degrees with the 12900KS, but adjusting for that warp was as least as important, so I suggest studying paste patterns if your cooling is not good.
