As a kid, Tony had always been on the small side. Almost diminutive.
So, his father told him about Captain America. Physical size wasn’t a perfect predictor—even when Steve Rogers was a ninety-pound asthmatic, Howard would say, he’d been all Dom and the serum had just brought out what was already there. He became the perfect Dom because he always had been the perfect Dom.
(Tony always thought that the moralizing, metaphysical mumbo jumbo was pretty far-fetched. He felt fairly certain the science of the thing would have worked the same way on anybody— the mechanisms of cellular rejuvenation and growth stimulation couldn’t actually look at the guy’s soul, for Christ’s sake… Even as a kid, though, he’d wisely kept his mouth shut on the subject.)
Howard told Tony that even when Captain America was frail, even when he wasn’t Captain America yet, he was a real Dom because he was always brave, assertive, and confident; he never backed down, even without the physical strength to back it up. That kind of inner strength marked him as a real Dom; muscles were overrated.
With a brain like Tony’s, mere physical stature wouldn’t matter, especially in a rapidly evolving modern society. Tony’d be able to project his dominance no matter what. It didn’t matter that Howard’s son was small. He’d be a good Dom anyway.
Apparently, the alternative had never occurred to Howard.