He did actually get taller, as a result of the “energies” in Karda Nui. From Bionicle Legends 11: The Final Battle:
" *“What now?” asked Takanuva. *
“Well, first we –” began Pohatu. He stopped when he realized he had to look up to see the Toa of Light. “Hey! When did you get bigger?”
“Fascinating,” said Kopaka, eyeing Takanuva, who was now several inches taller than anyone else in the room. “It’s similar to the way the Matoran of Light are taller than any others we have known. Perhaps it’s this place, the energies of it, working on their unique systems.”"
Regardless, though, I agree with what you and @Barafu have said; the official models don’t exactly have the most consistent scale to start with, and this model isn’t even official. It just determines the base appearance of Tuyet, which can then be reconstructed on a smaller scale later, if desired.