It seems to me that the lack of any substantial dedicated fight-book materials for the large High Medieval triangular shields has simply to do with timing.That's a perfectly good explanation as to why not much 'heater-shield HEMA' goes on. But let's turn the question on its head...
The vast majority of fighting manuscripts started appearing after 1400 - thus well-after the era of common usage of those things. By then, the high nobility had taken to full plate armouring, with only those little cavalry targes to be seen (cf. Gladiatoria versions circa 1425-50). Otherwise it tended either to be bucklers or pavises.
Why is it that most fighting manuscripts appear after when heater shields were used?
|Codex Manesse, a book of romance and chivalry from c. 1304-40|
This is a bit too much of a derailment to be brought up on HEMA Alliance in this embryonic form, but to me these are questions that the HEMA community needs to explore, especially if we want to engage with academics and institutions. Sure, they may not affect sword-swinging too much, but I feel that if you're not asking 'Why am I learning to swing this sword in this way?' then you're not trying hard enough.
|Codex Gladiatoria, an illustrated guide to breaking another person from the 1430s.|
Sod it, that's my dissertation fodder. Back to this essay.