Different envelope size printing

Is there any way to change envelope sizes when printing directly on them?

I've never used Shiprush for first class #10 envelopes. When I do a test print for "Letter Post", the print area is fairly small. As if there are 1.5" margins on each side.

I realize Shiprush seems to be designed more for parcels, but this functionality would be great. Way back when we used Endicia(not Shiprush), this was possible, including ability to just print stamps.

Thanks