Hp reduction on enemies when soloing

Anybody know the HP reduction in % of the enemies? I wanna know if it's worth returning or not. I'd bother coming back if it's somehwere between 15% - 50%.
http://onigiri.cyberstep.com/_/forum/
http://onigiri.cyberstep.com/_/forum/viewtopic.php?f=10&t=8909