In my experience these carpets definitely have some level of give for reshaping with heat, but successfully modifying to cover a greater area may be a challenge due to lack of available material length, or to maintain material aesthetics. Difficult to assess unless you have a carpet in hand to lay over the area, etc., I’m sure your hoping someone chimes in who has already installed the same tunnel and carpeted.
Nonetheless, you may consider that the reproduction carpets come in auto and manual versions. If I recall they look the same except for having the factory hump area being modified, which may or may not be beneficial for your application.
The factory floor pan is the same with just a pan hole cut and added hump, so in my mind a perfect fit and look might call for varying carpet material. Nonetheless I don’t know if factory originals were manufactured with more material, or simply achieved by just additional molding.
I wondered if the current reproduction carpet manufacturing included just molding differently, or molding plus different material (to cover varying surface area). I decided to pursue an answer and called ACC directly, and they told me they use the same carpet roll to manufacture both versions, so I conclude there is no inherent additional material in the manual hump area to work with when modifying at home.
Anyway, hopefully this helps in some way, good luck.
