Reduced the arm radius from 40 to 34, and redesigned the fillets for more strength.  To use it, you need to change the END_EFFECTOR_HORIZONTAL_OFFSET to 34.  This is as small as it can go without changing the arm separation, which might be a good idea, but that affects the hotends themselves.  I think I'd have to reduce the hotend rad to make any inroads there, which would further increase print area.