I can't really remember what the maximum height was I have gotten off a tank-packer-bump-thingy, but I guess it was around 90-100. But on average, I wouldnt expect to see someone getting much better than the 70-85 range.
Also there's the fact that the packer is "free"... (feel free to read on, but its just my unproven theories)
I've always thought that placing the packing in such a way so that there is a small ledge/wall in front of it would lead to better results in height and distance when doing these stunts. I don't mean a full 'wall', just some sort of structure that means the packer can't slide out (forward) from underneath you as you hit it.
Ofcourse that idea could be totally wrong, heck, one of the biggest distance ones I ever did was off a 'free' (nothing in front of it) packer. So maybe that means that having something in front only advantages the height, or maybe it means my theory is wrong all together, I dunno .
Alright, thats enough bad explaining, I think I'll just try it and see what happens