Agreed.... I think when we talk about pH in the soil, it is akin to a differential equation in which you have a dynamic process. The pH at any given moment depends on the amount of water, because the water will dictate the nutrients that are bound to soil particles or in solution. I would expect this to vary with rainful and evaporation. Maybe the pros specify pH in terms of parameters like water potential and cc's of water per liter of soil, or some such. pH by itself without further specifications seems an inadequate characterization.
I have thus far measured pH by collecting a soil sample and running tap water through the soil. I collect the flow-through and I look what has happened to the pH of the water before and after it was added to the soil. I only add enough water to get sufficient volume to measure with a lab pH meter. We can say from a liter of soil I add enough water to collect 20 ml. It is helpful, in a separate experiment, to weigh the soil before and after draining to measure the maximum water it can hold.
Dominic