I'm not sure if this has been written about in here. But if not, it may be valuable to others.
I came across something that I never gave much thought to before and I think I have the solution. I am using a countermarche loom here with 8 shafts. The way they are tied, is the back treadle hole is the one that sets the height of the treadle, the rest of the ties toward the front are slacker. So what happens when there are more ties on the upper lamms than the lower ones from the back treadle holes? Well the weight of the treadles on that upper lamm pulls the shaft lower than the rest. I figure the best way to solve this is flip the tie-up so the lamm has less free standing weight from the treadles to pull it down, by having a more balanced tie-up from back treadle hole to upper and lower lamms across the treadles. There are 8 connections to the upper lamm and 2 to the lower lamm. Quite an imbalance. The shaft will always dip a little from the others because of the weight on it, even when a treadle is pushed. You can adjust ties until the cows come home, the only practical solution I can see is flip the draft. Hopefully the ties are more balanced then, if not you have to shuffle a shaft in the draft that is more balanced. The back treadle hole takes all the weight of the treadle. I'm sure this has been worked out before, but never see it in the texts. I just finally took notice of what is happening. I just have a short warp on and am weaving fine, but not optimal. So something to remember next time.
Here is what an imbalanced tie-up on the back treadle hole causes to the back shaft. Too much weight on one lamm, coming from the back ties that carry all the treadle weight when free standing.