JKL keys strange behaviour on mac

JKL keys are used by most professional editing systems and are by far the quickest way to find accurately a frame, after finding approximately the position with the cursor.
But in Shortcut they could behave a bit better.
What they should behave: after stop, pressing “l” once starts playing at normal speed, and pressing it again should give 2x, 4x, 10x speeds, 20x (or similar).
Pressing “j” after stop should play reverse at normal speed, pressing twice 2x reverse and so on.
If the video plays forward 4x, pressing “j” reduces the speed at 2x, pressing “j” again reduces at normal speed, pressing “j” again stops, pressing “j” again plays reverse, pressing “j” again plays 2x reverse, and so on. The opposite thing if video is playing reverse and “l” is pressed.
This behaviour speeds up editing considerably.

on Mac osx 10.13.2 and Shortcut version 18.03.06 I see that some of the functions are correctly done (like single step and slow motion keeping “k” pressed and clicking or keeping pressed “j” or “l”), but the other can be improved. For example: pressing “l” once start playing at normal speed, which is correct, and pressing it again should give 2x, 4x, 10x speeds (or similar). It jumps at about 20x just at the second press, which makes this function unusable.
Pressing “j” after stop should play reverse at normal speed, but it runs at about 10x instead.
The JKL keys are very important, if they work as they should the job is done quicker and better. Is there a way to change their behaviour?
Thanks a lot!