Every fader (volume/gain, panorama, send fx and etc) in TM FX can be controlled via the mouse scroll wheel.
The most frequently used fader is probably a gain fader (inputs, outputs, etc).

The problem is: the most frequently used gain fader scroll zone is too tight, it is quite complicated to get into tight strip by the mouse cursor every time you need to adjust it by scrolling. Of course, there is a another way to do it - simply by clicking or entering the correct gain settings. But many users do this by scrolling.
So the suggestion would be: to make gain level adjusting zone wider by sharing it with the level meter. So if you point the mouse to the level meter zone and scroll - the gain fader would be also effected. So it would be easier to blindly adjust every gain level, and not "to aim" precisely as it is implemented now.