Forget about the picture.
So your using a router machine to "mill" and just let me say that
you probably do not have the rigidity of a milling machine.
Don't expect milling machine tolerances. The whole "system"
as applied to the machining task comes into play and is also dependant on the material your working with. So I will repeat "YOU have what YOU have" and it will only do what it can.
So do some testing both in the material you are working with, how the code is done, tool used, etc and see what it can do.
If you want better than what it can currently do then you need to look at each part of the system for possible improvement.
RICH