This definitely sounds like you have a low amp battery that is not able to deliver what the mod is set to.This is interesting I would have never thought of an RTA producing clouds, I'll have to look into that, for your mod what are you using? when did you say 88-90 watts are you delivering that much to the coils? because when I fire my mod and set it at a higher wattage it doesn't fire at that range and fires lower, for example, I could set my mod to 100w but when I press the fire button it reads 9w on the screen when I know the coil I build can handle more, I checked using steam-engine, this could also be an issue with the subpar battery I'm using
I like two cell 18650 mods for anything over 60 watts, batteries last longer sharing the load.
I do own two Grus mods though. They are not the hardest hitting mods I've had, but with decent batteries they are ok.
As far as an rta producing clouds, that all depends on the airflow.