Fuzz Circuits and Volume Drop Problems

[Bishop Vogue]

Hi all, hoping someone can help me to understand an issue I discovered by accident.  I've been building pedals like crazy recently, and always test them on a small EVJ + Vox cab that I keep at home.  Recently I scored a good deal on a Fender m80 and of course I wanted to try my pedals through it.  This is when I noticed a massive volume drop/tone suck from many fuzz circuits (bazz fuss, red llama, zvex woolly mammoth, others) while other pedals that were not fuzz sounded good (zvex SHO, orange squeezer, lotuspedal snowjob).  Asked a buddy if I could bring my collection to his rehearsal space to try the units out at full volume and when I did, the problem was even more pronounced (also quite amazing to hear which circuits sound great when played at stage volume).  Has anyone else encountered this issue?  All I could think was: thank god I didn't sell these pedals... my customers would have complained and I, not knowing any better, would not have believed them!  Yikes.  Why would a circuit work well through a tube EVJ but not a tube tiny terror or solidstate m80?  I can't figure it out.