How big are the Warlord humans? That Silence looks like a basketball player.
I didn't get any of the Dr + companions sets, so I can't say - I was a bit afraid they'd be out of scale compared to other human models, so I just got the aliens.
The Silence are tall and thin in the series, so it's not that much of an issue - in fact I am counting on the fact that as these are all alien species the scale is not a major problem. But I'd guess (and I emphasise I'm guessing) the humans could be taller than 28mm.