Help with font used in combo box elements

I’ve created a modified skin for my combo box - I basically wanted all the elements to be twice as large so I can accomodate a touchscreen user (with fat fingers). I did that by editing the HaloTheme scroll bar assets and combo box assets. All this looks fine, except for one thing - if I increase the font used in the list of items in the combo box, pretty soon the font gets too big for the bounding box around each item. The letters get clipped.

It sounds like the bottom part of a combo box is made up of scroll bar assets and a “RectBorder” object. My question is how to control the size of the RectBorder object if that’s where my problem lies. It doesn’t scale to accomodate my choice of font?

Anyone know how to make room for larger fonts in a combo box?