Honestly I'd describe a guy like Tua as thick. Big certainly, despite his average height, because his whole body and all his limbs are incredibly thick. I don't see how that is frame at all, we must have very different ideas of what frame means. For example wald pussy has a fucking huge frame, he is very tall, but also wide, broad shoulders, huge reach etc. Tua basically has more meat packed onto a much smaller frame. Who would you consider to have the bigger frame out of those 2, at the same weight?
It's the thickness of the bones that determines how much meat a guy will naturally carry tho (thats not conjecture on my part, its a cromulent fact). I just think of frame as a guys bone structure and how it effects what lean weight their body gravitates towards; differences in shape like reach and so on are just that - maters of shape rather than size. If a forensic investigator found Tua or Tyson's skeleton they'd be able to tell that they were huge. But i definitely agree we could talk about a 'functional frame advantage' in boxing and Wlad definitely has one over Tua::
Interesting, that is simply what I would describe as size. I think of frame more literally, as the area they occupy just by looking at them, combined height and width. Which of course disregards bone thickness, muscle mass etc. The more I think about it, the more I think wingspan is part of frame too. I see frame almost like the combined length of all your bones. If a guy has 10 inches more wingspan than another, it's almost like being taller, as there is simply of you to distribute weight - num sen? To put it simply, by your definition I don't see any difference between frame and size.