Personally I'd just remove the screws and wedge metal shims under your plywood to force it up then lock it back on place.
Im facing the same issue. There so many 50/50 Ideas against foam or mat or shims. This is a Aqueon 210 rimmed. Left front corner has a gap but the tank over all is level. So from reading, this should be shimmed at the stand? Or at the the bottom of the tank?
I've been through a tank crack from stress - trying to avoid that again.