Soil Vent Pipe regulations

As I understand it, Part H requires soil vent pipe stack to be 900mm above nearest opening window. In my case, the soil vent pipe will emerge through the roof near to (about 800mm but not quite sure yet exactly how far from) a new opening Velux window. If I make the stack 900mm high it will (a) look ridiculous, and (b) extend above the ridge line.

I have flexibiity to move the "emergence" point of the soil stack to some extent but limited laterally by proximity to nearby dormer window set in the roof. I'm not sure how to interprete the regulations in my case. Please could someone advise?

Thanks