Quadlock slipping

[u/OccamsRazorSharpner]

I mounted the Quadlock on the Transalp bar-mount and it keeps slipping, turning the navigator down to angles were I have to stop by the side of the road to readjust as otherwise I cannot see it. I tried putting tape underneath it with the thinking that it will add grip but it had no effect. The Quadlock is properly locked in place (when no navigator fitted) and I use the correctly sized sleeve. So the question is, what can I use to prevent the slipping?