thats good to know. I can't find the video now but I am pretty sure the US military in around 1950 decided that you should use a 2or 3 foot grounding rod for doing a field ground for a munitions inspection, retrofit and disposal operation under field conditions. Basically they just had the powder boxes grounded (where you empty the propellant from the shell).
This is the video but I rewatched the part where I thought they mention it, and they just said it should be grounded without telling you how to ground it, maybe its in a diff video or another video or in another part, I might watch the whole thing again if I am bored but I am pretty sure the military said 2-3 feet some where.
I doubt a 2 foot rod will hurt anything right? It's reasonable enough to carry and feels proper. But I think I understand what you are saying since the body resistance is like what 150k, the resistor in the strap is 1 meg and the mat has a high resistance too, so it should become equipotential quickly.
Is you assertion still true if you have one of the blue/black mats, where the top is very high Z and the bottom is more conductive? The heavy duty rubber ones that are very tough and expensive.