I think the issue lies not in the imprecise use of RM cats, but the imprecise useage of the real world. . .the RM categories define by size and utility, while there's a lot of fuzzy in the size and shape distinctions of the shield terms you're using from real world sources.
The wall Pavise, since it's not worn, isn't a shield at all, it's a somewhat mobile peice of cover. . .if you don't wear it on a limb, I wouldn't consider it a shield at all. . . .it's a peice of mobile cover designed to be moved around, but once it's in place the user lets go of it and just uses it for cover. . .so for a pavise I wouldn't use the shield rules at all, I'd use the cover rules. . . .The same as I'd use if a PC ripped a door off it's hinges, walked at an enemy hiding behind it, then stuck it into the ground.
If it's a "strapped to your arm" pavise or a rectangular Scutum it's a Wall Shield IMO. It offers full body coverage, can be interlocked to form a gapless wall, and also missile protection not only from dead ahead, but from the angles to either side of dead ahead also.
A kite shield covers you ankle to head, but due to it's shape wouldn't offer you good missile cover from angles other than due ahead, nor could it be interlocked to offer a true shield wall. Same is true of the Oval Scutum. . .they'd be full shields.
Rondache come in so many sizes, to me it comes across as "Round shield" which covers a lot of ground from Target to full.
Heater/Parmula fit the normal shield logic, though again the latter tend to vary a lot in size and could potentially be full or target shields depending on size.
Target/Targe shields are meant to be actively used for parrying more so than either blocking or covering, so I think would cover bucklers. . .but if a Heater, Parmula or Rondache gets small enough it could be a target shield.
The chaos and confusion lie in the real world, and the way shields of the same name varied by region or era, not the rules side.