Bluesideup
You are quite correct in that I do not trust the automatics. I have always tested the automatic cut off at start of refuelling but I am aware of several cases over the years, one very recently, where a fuel system rupture has happned; Probably due to exess pressure or hydraulic hammering during refuelling.
It is true that you need to know the bore of the pipe but I am not clever enough myself to work out flow rate along a known bore pipe into pressure.
MM