For a slight increase of speed your choice was certainly correct I’d say.
That sounds as you would expect some kind of function which is not really planned.
However - looking at the mechanical function of the carrier connection (to the seat mount) it seems that you can not simply tighten the bolt 370 harder to get some friction (and your desired effect) into that joint!
For my meaning (knowing that “Ming cycle” and “precision” will never meet) I’d assume that the two latches for bolt and nut are a little bit too far away from each other.
When you move the rack over the plastic seat mount (without bolt) - does it have much play there?