In general, as far as I have learned, moving the MB changes the shape of the breakpoint. On a strong mass bias/PSA ball, an MB only 3.5" from PAP will provide more of a hook and set reaction. To make the backend sharper, place the MB around 4.5" - 5" from the PAP.
If you like the midlane read, then I wouldn't change the pin or the surface.
The sharper backend should also give you slightly more backend. Whether it's enough to satisfy you is unknown.
--------------------
"None are so blind as those who will not see."