@Discorde: thanks for the copy!
Regarding
A simpler procedure would be to set local QNH for the whole flight, resetting only if the QNH changes
: yes, if "local" QNH were universally available. But it isn't always. So I am afraid "regional QNH" is the least unfortunate that can be done. And it works reasonably well, in reasonably flat areas. As for discarding QFE: yes of course. Those funny Brits are alone to want QFE, anyway; and not even all of them.