I had the same Tektro levers years ago, never got along with them. I tried to modify them a bit, filing the surface that's against the bar, got them to sit at a slightly better angle. Then I took a bit more, and more, until the clamp stopped working.
Not only does this Grepp tape keep unwrapping but I still haven't sorted out the hood angle on my Surly.
Posting to invite some abuse. That will provoke me into finding some broken Di2 shifters I can turn into comfortable drop bar levers.
(On this, is it just my imagination or do these Tektro levers not play very nicely with modern drops?)