Yup, HLS is ridiculously fickle in that regard. In our lab we had the case that swapping out a C-style array T[] for a C++ std::array 10x-ed our resource consumption with no explanation.

And also the general problem of scribing resource use to the different components isn't easy, because thz way control flow is structured heavily alters that

Of course, that's what I'm trying to fix with SUS :p