Maybe it's just me but if your EOTech is able to move on the rail when dropping the charging handle
then it's no where near tight enough. Either that or your rail is way out of spec.
When mounting my 552 I place it on the rail, push it forward as far as it will go and tighten hand tight and then use a coin to tighten it another 1/2 to 3/4 turn. This is probably tighter than what EOTech recommends but it works. As of late I also put a drop of blue Loc-Tite to ensure that the thumb screw does not loosen up on me.
As far as Loc-Tite goes you may be able do without it but if you shoot a few thousand rounds the EOTech screw will eventually loosen up, maybe in even less rounds if it's not on tight enough to begin with. I very rarely remove my EOTech but even with the blue Loc-Tite it's still pretty easy to remove it when needed.
I've been using the EOTech 552 since Rev D and over the years these are things that I've found to keep my EOTech mounted securely, YMMV...