I've been using a Permobil C500 Lowrider for 10yrs. Yesterday I received my Permobil F3 but ran into an issue that it sits to tall. (Permobil discontinued the lowrider.) I'm 6'4 so now with this chair my head is in the roof of my 14" dropped floor van and my legs are too close to my handcontrols. I've been using J2 cushions since 2000 with no skin issues but they asked if I'd like to try a ROHO to maybe sit lower. I'm needing to sit 2 inches lower. My C500 measures 16 from floor to seat pan where my F3 is almost 18. My rep asked if we could run a smaller rear caster but Permobil said no. Any suggestions?