brakemeister

I am not a engineer... :-) and even if .. it would be difficult to say if the extra material which you cut off above the clamp, will have any effect.
The knob is there for general guidance when you have to loosen the stem in order to fold it. Its not designed to keep the bar from rotating ... it will do that to an extent obviously,preventing the bar to fully swing around.

Whats definitely not designed for is to have a bullhorn bar on a height adjustable stem ... that together with sprinting standing up mashing the gears is definitely the reason for failure...

I am positive that a Jetstream T one piece post will be the answer...
best Thor