Replying to Backyard pvc vs. metal rails at mountain

For some reason i can whip around 270's off pretty well on pvc and then when i get to the mountain i can't get shit.  i can get bs and fs 270's out on the pvc most the time and sometimes when im sliding unnat too.  not every time on command or anything, but a lot.  do you  guys think there is a reason for this?  any tips?  has this happened to any of you guys?  also  while i made a thread, i might as well ask for some 270 on tips.  i got it on boxes at my mountain, then all of a sudden i can't get it again on the same box a few weekends later.  im going to try it on the pvc rail in my friends backyard today.  just go in normal, pop then spin, look around with my head and spot the rail, land. sound right?