[Kurfürst]

Thanks. You can find the report on the 109lair, I think along the tail unit changes stuff, but if not, I can email you.

As for why the change, I don`t know, perhaps because the undercarriage was to be fully retractable and covered on the 109K. Dive limits are more of a function of aerodynamics, rather than raw structural strenght..
But there`s more conservatism involved imho than pure technical neccesity - it`s enough to look on the fact that all 109F and G models, despite quite a variaton between them aerodynamically, had exactly the same dive limits.