No way! You do need them high up. Having them on the floor would definitely introduce comb filtering. But you also don't want them /exactly/ at ear level if you like to keep your hearing, because those speakers are capable of some massive SPL and the way mine came, they needed some serious modification to the signal chain beyond the electronics there, in order to get rid of the noise from the line level crossovers. You need to gain-stage so the crossovers have maximum headroom within your range of listening levels. In that tiny room in the picture, the hiss was probably extreme. Especially with all that glass.
You can't angle these speakers. The amount of hardware you'd need to do that would be immense. A bunch of metal that would resonate at high SPL. You don't want that.
Those are not monitors for a live concert. Live monitors are there just to let the musician know if anything of them is making it through to FOH. Reproduction quality is not a concern at all. That's why those things always ultimately sound like crap. $100k speakers like PMC's have vastly different objectives to live monitors. No reason to bring up live monitors at all and how they're hung from the ceiling sometimes. That's like saying "well, with this Ferrari, you could get some nice big threaded wheels, they work on a tractor". No way...