In the end, I came up with something myself and wrote it.
He was very small.
Drift couldn’t look away, but he forced himself to lift his gaze lest the bot caught him watching. That was even more embarrassing, if you thought about it: if he was Magnus, Drift would be looking at his chestplate. He would definitely not be avoiding the sight of a green face, a facial insignia, frown that appeared when he saw Drift.
He heard about it, but he never even imagined how it must look - how much smaller Magnus (Minimus?) must be. He’d heard of loadbearers, but to see it like this– he probably wouldn’t even think that this stranger was Ultra Magnus, but his aura was impossible not to recognise.