Figures are not usually measured sole to eye, so I think I understand why you say these figures are 1:43.
But a figure measuring 38mm head to toe, using metric conversion, is 1.5 inches. In O scale (1:48), 1.5 inches = 6 feet, the typical height of a hero figure (or average adult male) who is standing straight up.
Naturally, if a figure is crouching, and it still stands 1.5 inches, you could guesstimate it's closer to 1:43.
Again, for those who seem to not have heard this before, when you are talking about O scale, a distinctly American shorthand reference, it is referring to 1:48, or 1 inch to 4 feet. 1:50 has no scale name. Europeans are more apt to model 1:43, which is also not typically called by a letter scale. 1:43 is the traditional European proportion for O gauge trains. Gauge is the distance between the rails, and that's where the letter names Z, N, HO, S and O came from and over time were applied to the proportionate scales associated with each gauge. (Technically, we should say 1:87 scale trains run on HO gauge track, but no one says it that way anymore.)
Anyway, I picked up some of the Harry Potter figures as well as the Nano Spider-Man, Guardians of the Galaxy and Avengers figures, and they are all well done and close to 1:48. I now have too many options for Harry Potter scenes, but appreciate the tip nonetheless.
If you want to dramatically add to forced perspective, you can add the new Harry Potter Gringotts Bank that Hallmark released in July. It measures something close to N scale, though I have no idea of the dimensions of the prototype because I can't seem to find my way to Diagon Alley.
