@yuriv @csglinux I'll try varying the insertion depth, but it seems like there is quite a bit of amplitude despressions around 6-9k compared to other rigs (as can be seen from my MH755 measurement). Another issue is with tip fit on the coupler. I use smallest MH755 tips because they fit the best, but still slides over time. I don't know how to keep it stable besides having something holding it in place. Varying the depth and keeping it stable for precision will be a challenge.