Here by me it's a mix, and looking at it, it looks as if it was decided according to the building design underneath the pad.
...and as for...
The anal compunction of some drivers to align their machines (especially skid equipped) with the edge of a square pad regardless of the wind direction is notable.
I looked underneath some of them and all the strong structure support is in the middle of the pad and not at the sides. The pad is designed for ONE helicopter (CAT A) at a time, so be carefull where you park your bus...