Ground effect adds a 'cushion' of air under the whole heli. This can make the heli very unstable or conversely very stable depending on the given situation. The TRex is a very light heli easily effected by air currents as well as wind. A good pilot can overcome this, it is a challenge.

We can carry this out further with this elaboration. I like scale flight. I happened upon some big electric wire spools, that are about 3' in diameter when used as a table. In calm conditions, as I come in to land over the pad, things get funky as the front of the rotor disc begins to be directly above the table and the whole heli dances all around until I get the entire rotor disc over the table. The part ground effect and part out of takes great amounts of fast pitch changes to keep the heli stable.

Now, with wind/breeze this may not happen because it is the same as being in forward flight where you get translational lift which you perceive as less collective. Helis like to fly in forward flight much more than they like to hover. Extra lift. \

hope that helped