I vaguely remember some designer comment that it was deliberately turned up to 11 ... ahem ... 16 to give a CCV player pause.
Which it should. The 16FP isn't a measure of how many steel shards the round can expel or how big the detonation is, but rather a measure of how likely a squad of men would be to stick around once it went off. There is no quantifiable measure of this, unless someone wanted to find AARs that reported in detail what the men's morale was like after an encounter with an enemy tank actually firing the thing.
There *were* post-combat interviews in the American and Canadian armies (I presume the Brits did as well) which asked troops to rate the 'scariness' of particular enemy weapons systems. I'd be surprised to see the 92mm grenade projector get special mention, but am open to correction - if only for no other reason that close combat with tanks had to be very rare in 1944. Yet another reason to make the 16FP feel 'right.'
Having said all that, the Americans had (and still do) a very "not-my-job" mentality, such that when you specialized at one thing, that's what you did. Thus drivers are not trained to fix engines in their vehicles. Here, half our driver's courses are consumed in mechanical instruction. Which again is a way of saying that infantry should be expected to decline close-combat "opportunities." And one needn't take my word for it - I believe Mark Nixon or one of the esteemed quoted such a passage from a British regimental history in the General back in the days of G.I., in which a U.S. engineer officer came under fire and un-assed the area he was working in, to the surprise of the British. He didn't say "not my job," but that was the impression the anecdote left me with. It was used as an example of the kind of thing that informed the design. One can look at official U.S. tank/tank-destroyer doctrine for another example of this culture (which doesn't seem much different than the British approach either).