Pretty sure he's undersized, the original hulk premium format was not supposed to be exactly 1/4 scale. (I think I've read in the original forum thread where the artist had to scale it down a bit)
And when comparing the original hulk pf and this one, this feels smaller. So I'd put him definitely around 1/5th scale. After seeing him with the rest of the avengers, he doesn't feel as big or as intimidating as he should be. Unlike the hot toys version, you could see he's massive compared to the rest and supposed to be the giant that he is.