A handy person from Memphis says:
May 10, 2016
Assuming they fit within the window, what would change if I used an operator with a 9"/11"/13.5" arm instead of a 9.5" arm?
Tom from SWISCO responded:
May 11, 2016
The window sash would likely not be able to close or open as far, in some cases preventing the window from closing at all, depending on exactly what the difference is and what kind of sash you have. We recommend sticking with the same size you have now.