FOH can also be the jack@$$ sitting out front who can make you sound terrible. Back when I was touring and opening for someone else, bigger act than we were, there was a term we used for what happened to you. We would say, "the friggin' soundman lunched us..." Meaning he made us sound crappy so the headlining act would have all the power and authority of the sound system.
Yep.. seen it, been on the receiving end.
35 yrs ago - when I was a young impressionable muso - my very first "band" got to open for a world-known Brit 50's-revivalist band (who shall remain nameless to protect any innocents who were not part of the band back then.. Yes, they are still going) who were on a world tour. Obviously, we were stoked, fired up and practiced like crazy!
Apparently, we were too good to be their openers. They were all back by the console (at the back of the 3,000 seat hall) during our sound check, watching us. We saw them talking to their crew before we left to head home and change.
Miraculously, our tuner and practice amp, were "missing" from the green room when we arrived back. Miraculously, the opening song and all the rest of our 45 min opening set got FULL WHITE light on the stage. No LED's back then.. Stage full of Par64 cans - all cranked. The heat was bad, so everything de-tuned. Oooops.. No tuners. The monitor mix was completely [and deliberately] hosed, so that there was nothing useful in my wedge. When you gesture at THEIR monitor eng, and you get the "I can't hear/don't understand you" type of response <shrug>. Full theater size stage, and I couldn't hear the lead singer standing 6-feet away. Couldn't do harmonies except from memory!
We SUCKED!
We were not experienced enough to recover very well, tho we did try.
It was highly EMBARRASSING in front of our home town to be deliberately sabotaged to sound so bad !! 
What do you say??
I learned from that, and we later heard feedback from other stops on their tour where the local band go the same treatment.
My first exposure to the nasty side of music.