Added thoughts that might, or might not, help you. It would seem to me that the finished HRT size is more important than the angle since you have to choose one over the other. If you agree, here's some valuable info on how to work with HRT's and the somewhat unique problems they pose. And, as luck would have it, the example is an unfinished size of...drum roll please...2.5" x 4.5".
http://www.quiltdesignnw.com/PDF/HRT_2x4.pdf