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Is WOT High Vac or Low Vac condition in the manifold?
Does full closed throttle produce the highest level of vacuum then?
I think this is the case as if you step on your repeatedly step on the brakes while accelerating the pedal get stiff quickly (IE booster does not have vacuum to assist braking).
This would mean that the time that the manifold is closest to being at atmospheric pressure would be WOT correct?

So on the a fuel map row 10 is the highest load/low lowest vacuum condition?

If this is the case is the reason that ITB have a hard time using a Map based system is that they loose vacuum sooner with less throttle and therfor produce a low resolution signal with no usable resolution past a certain throttle position?

I feel stupid but I never really gave any thought to this at all...

It is absolutely the case. When throttle is closed, the cylinders draw a vacuum on the manifold, and the volume of the manifold affects how quickly the vacuum is lost when throttle is opened. WOT reaches closest to zero pressure (Atmospheric)