Back to J'onnz.
DC seems to have realized that MM having the ability to grow bigger and stronger might prove TOO Deus Ex Machina to create plausible tension in a story after awhile. Who could stand against him?
So it seems they QUIETLY began imposing limits on J'onnz.
Note that, by the time the 9th issue of that series rolled around, J'onnz was complaining about the stress of changing the proportion of his "Martian mass" for "Earth mass", whatever that means, even though J'onnz had substituted a literal skyscraper's worth just 7 issues prior.
Note that they impose no such limitations on J'onnz's green Martian counterpart, Malefic, however: