^^ Interesting. The reason your 14x16 experiment felt like it had no sweet spot was because you re-tensioned used string and it is not only completely dead, but also freshly tensioned. I had a new multi string job that I hated, in old racket that I didn't care for, so I mounted it on a 6pts mount and pulled it all out. I restrung it in a smaller headed frame and it was totally dead and harsh, like dead poly! If even an almost new multi became harsh then a poly/kevlar with even less elasticity would most likely be the same or worse.
Now how about that spagetti pattern?