Atom power was his small size, but, here are a few exceptions to that from the Silver Age with art by Gil Kane.
The Up And Down Dooms Of The Atom
Here, Ray Palmer is paralyzed by being struck by a beam in a laboratory accident. The accident also gave Ray telepathic abilities, and he contacted his fiancee, lawyer Jean Loring, to activate his shrinking belt....and thus Ray shrank...out of sight.
Sometime the smallest guy in the room can make the biggest difference!
Trouble At The Ten-Year Club
Here, scientist Ray Palmer meets with 10 fellow Ivy University graduates from his class, all bringing back an item to the reunion from their current profession, except for Jack Archer, who sends a note saying he will steal the other nine objects.
The Atom NOT being in costume at full size saved the day here for Ray Palmer!
JLA Giant) where Atom was larger than his team (making Ray a giant member of the Justice League)....
Calculator, or when Atom was searching for Jean Loring in Super-Team Family, they show (properly) Atom being Ray Palmer when he was around his teammates in his full size!