Kirstey - your pants are well in order and are not talking for you. The RPS is the lowest forecast "QNH" for the WHOLE region and as such covers all those points that are normally used to measure the QNH.
It is a forecast, not a measurement, and so does not need to be "taken at a point" as the actual QNHs may not even get that low - it is just the most pesimistic guess (sorry, estimate) that the met man can come up with.