Clip edges to grab are too small on 4K monitors.
on 4K monitors, the mouse is moving in the same mode than on 1920x1080 (similar time to move ta angle to angle) and with these new kind of monitors targetting the EDGE of a clip is very difficult (it's necessary an high dpi and high quality mouse to be sure to not re-try 2 o 3 times before taking the edge.
i think that this edge is and hardcoded number of PIXELS (3? 4?)
if i can suggest ... the hardcoded number of pixel can be increased by the ZOOM FACTOR of timeline.
11/21 4 pixels
12/21 5 pixels
13/21 6 pixels
14/21 etc etc...
or something like that
this is just to speed-up jobs on larger (or longer) screens.