A proper 1/4 scale Predator would be around two feet tall, based on Kevin Peter Hall's 7'3" height without the suit. This is the same height as a human character in 1/3. That might be why it gives off the vibe of a larger scale, but not quite.
The height measurement for the City Hunter wall mount (equipping the disc instead of the spear, which should make the head the highest point) is roughly 31". From a side view, the character seems to take up 55-60% of that height, putting it at 17-18" in a crouched pose. If he were to stand straight up, he'd be at least two feet tall as well. My assumption is both are 1/4 scale, but a confirmation would be good. Still, with one in a full crouch and the other stepping on a rock, you may be able to get away with displaying both even if they're not a perfect match.
Historically, most of our Predator and Alien collectibles haven't been properly scaled, so we are used to seeing undersized versions of these characters. If Prime 1 is going for true 1/4, this will appear to be massive. I can't even imagine how tall their Aliens will be. A 1/3 scale Xeno would be just a few inches shorter than a 1/2 human.