Regards to sizes:
I want to point out that the Panzerfaust 3 and RPG-29 can have warheads ranging from 60mm to 90mm caliber - a tad bigger than ark's guesstimated size, but still fairly smallish.
I'd also like to point out that the original Panzerfaust was utilised in like manner to the Marriage's weapon; in this case instead of the user holding the tube, the tube is built-in.
I'd also like to point out that the Panzerfaust was capable of killing tanks of its era, and that it had a fairly small warhead - the shaped charge was only 800 grams, the rest of the weight of the weapon being propellant, casing, etc; and had a speed of 45m/s. Which meant that for ranges in excess of 45 meters it would take several seconds to travel the distance (admittedly it lacked sufficient propellant to do so - typical engagement being either point blank ambush or from about 60 meters).
So a weapon taking several seconds to hit? Doesn't nescessarily mean anything.
Also, regards HE and HEAT:
Using HE as a catchall term isn't accurate as there are various means of using high explosives to defeat armor.
High Explosive Anti Tank is the most common: essentially a warhead that when it detonates, forces a jet stream of metal to punch through armor.
The point about HEAT rounds being less effective on living bodies is probably due to the fact that a human body won't have enough resistance for the warhead to make contact and detonate - it'll just go through the body.
High Explosive Squash Head is a bit different: it uses thin metal shells filled with explosives and a delayed action fuse. The warhead hits the target, the explosive is squashed against the surface, and then the fuze detonates, resulting in transmission of a shockwave through the outer surface and through the tank.
What that means is that the outer armor remains mostly intact but a shockwave is transmitted through the armor along with
spalling, causing damage and killing the crew inside the vehicle.
What's pertinent to this discussion? HESH rounds are fired at lower velocities to maximise the amount of explosive sticking in on point, rather than being dispersed from a high velocity impact.
Generally speaking though, using both types of weapon on a human body, it's debatable as to whether the human body would be able to set off the triggers. Though as with the .50cal Raufoss HE/API round, even if the explosive isn't triggered, you've just been hit with a large warhead - the explosion is the least of your worries.