Constant sized rehersal marks?

[Steve Lacy]

Using "\set Score.markFormatter = #format-mark-circle-numbers" how would one go about making sure that all the rehersal marks are the same size (i.e. the radius of the circle is constant and the font inside scales to fit, and digits are centered within the circle?).  Here's an example score that I would like to fix:

(http://lilybin.com/qurd93/2) 

Additionally:

- I find that the "1" inside the first rehersal mark needs to be tweaked to the right a little to be visually centered, 

- The "10" looks unnatural and needs some kerning so the digits are as close as the digits in "20" and "30" are

- The mark for the "2" and "20" would look better with more default padding as the lower left of the digit almost touches the surrounding circle. 

Steve