The thing about rotary is that they are steps per degree. Not full rotation.
For example, I have a Chinese rotary axis that is a stepper with 2 gears and a belt.
It is a 1.8 degree stepper which has like yours 200 full steps per rev. No clue what the belt drive ratio is. Micro stepping is at 10.
So to tune it, I started with a number, lets say 100 steps per.
Zeroed te A axis in mach. MDI G0 A360
Watched it rotate. If it went to far then the steps per for A is to big. Not far enough, then steps per is to small.
After each steps per change, you must SAVE AXIS SETTING.
Zero A axis work coordinates because it will change. Then repeat the MDI.
Your 3.3 steps per sounds close to the right ball park. I think I was in the 10 steps per range.
There is no logical reason why the steps per cannot be that low. Just type it in I just did it as 3.333 and it took the setting.