hpg rear shocks stiffness

so i got hpg shocks for my xmr and getting rid of the air system, got the hpg shocks installed, and to my surprise from what i read, the front seems really good, pretty happy with the way the front turned out, stiff enough. (i like it stiff don't like sinking in when accel or brake. but the rear, the rear shocks were noticeably shorter than stock air shocks, front where actually really close to the same length, so back to the rear, little shorter i can live with, but I'm 250lbs and 140 lbs gf like riding once in awhile to, but just with me on it alone it squats to much for my liking, do they make an hd spring for the rear. should i be able to put a pipe spacer in the shock to stiffen it up?