Exactly, or have an issue at idle and run good on midrange and top end.

The ST sometimes exhibit this. You can adjust for one but not both.

As you said the most probable cause is an air leak. While typically the prime suspect is the "O" Ring seals of the Carb, with SuperTigre engines, that is not the what is the primary culprit.

Rather the throttle barrel cylinder ingests air like CRAZY, which is why SuperTiger installed those rubber "boots" to help seal this area.

( I took a brand new replacement carb that I got trying to solve these problems, then after closing off the intake area with a stopper/seal I put a vacuum on the engine side of the intake "O". Copious amounts of air are drawn in around the throttle barrel cylinder at the "boot". )

The problem is that the boot lets in a lot of air. To overcome the problem you end up richening the engine a lot to get a good transition, but the low end bogs down...

Some people suggest using a second party carb to solve the problem... ( A Perry Carb cures it quickly...) but I'd like to see both a "user" fix and that SuperTigre do something about all of this.