Lyxen
Great Old One
"Harkening back to the example of Rasputin, it would be safe to assume that he could withstand physical damage sufficient to have killed any four normal men, i.e. more than 14 hit points. Therefore, let us assume that a character with an 18 constitution will eventually be able to withstand no less than 15 hit points of actual physical damage before being slain, and that perhaps as many as 23 hit points could constitute the physical makeup of a character. The balance of accrued hit points are those which fall into the non-physical areas already detailed."
Hmmm... This was a very hypothetical computation, especially seeing the rest of the paragraph: "Furthermore, these actual physical hit points would be spread across a large number of levels, starting from a base score of from an average of 3 to 4, going up to 6 to 8 at 2nd level, 9 to 11 at 3rd, 12 to 14 at 4th, 15 to 17 at 5th, 18 to 20 at 6th, and 21 to 23 at 7th level. Note that the above assumes the character is a fighter with an average of 3 hit points per die going to physical ability to withstand punishment and only 1 point of constitution bonus being likewise assigned."
So, basically, it's a one-off computation for a single 7th level fighter. But I agree that it gives and idea of the rationale.
The PHB.
"Dungeon Masters describe hit point loss in different ways. When your current hit point total is half or more of your hit point maximum, you typically show no signs of injury. When you drop below half your hit point maximum, you show signs of wear, such as cuts and bruises. An attack that reduces you to 0 hit points strikes you directly, leaving a bleeding injury or other trauma, or it simply knocks you unconscious."
It says typically show no signs of injury, because if the PC is bitten by a giant spider or stung by a scorpion and is still above half hit points, there would need to be some sign of injury for the venom to be able to force a save.
And I guess it would be less than 50% are meat, really. Below 50% and above 0 would be a combination.
Note that this is very indicative only, not only as you mention, but also because it's not even a rule, it starts with "Dungeon Masters describe hit point loss in different ways" and includes "typically".
So I guess we stay in the same idea of ballpark combination, which makes sense since, although various editions modified the descriptions a bit, the concepts stayed very similar.