In case you find a source code example helpful:
Here's a link to some
java drive subsystem code that's based on Ether's Inverse Kinematics equations, there are some coefficients in there for the wheel base (length and width) as well as for wheel diameter that account for the issues being discussed.
This code also has optional field-oriented drive in it as well, and support for speed control via quadrature encoders ("traction control"). Team 2465 has found both of these to be helpful, and think they're useful for this year's game. This code is written to work w/black Jaguar motor controllers.
There are other examples posted on ChiefDelphi that you'll find, too.