What do you mean by tremolostem. I have not shown example with tremolo.
Also, what slope rotation, what real slope?
What space and length fraction, default StemTremolo, not sure what is that 'default'.
The stems for the notes are slightly different - actually quite different - especially when different note duration of voice happen to be close on top of each other, as in my system they can be differentiated by separation of hands (in piano, but it is valid for any instrument that uses hands... probably all of them).