Bobby,

I believe the behavior you are describing would be for an absolute pressure controller (not variable).

The variable absolute pressure controller allows a moving target.  The way the one I have is adjusted, the minimum setting of the variable function is set at 28" Hg and is referenced to the duct between the compressor and throttle body.  The wastegate is closed at pressures less than 28".  Advancing the throttle enables the turbo to eventually develop pressure which is initially limited to 28" Hg upstream of the throttle body by the controller modulating the wastegate.  So MAP is controlled by the throttle up to that 28" Hg.  With normal atmospheric pressure here of 23" Hg at 7200 ft elevation, WOT would only give a MAP of 23" Hg without the turbo.  With the throttle open and MAP at 28" Hg, the variable function of the controller can then be actuated with a separate control cable and used to raise the MAP above 28" Hg.  The maximum attainable MAP is determined by the adjustment of the controller or the capability of the turbo. 

With my equipment, there is still throttle movement available when 28" Hg is reached (the throttle body is larger than necessary) so the throttle body linkage could be also directly connected to the controller instead of using a separate control cable.  That way the single throttle control would enable setting the MAP from idle to the maximum allowed by the controller.  I don't know what the upper limit of MAP is since 36" Hg is the highest setting I've tried.  My intent is just to normalize MAP to sea level.

With this control mechanism, above 28" Hg the turbo is only producing the amount of boost required by the throttle setting rather than producing excess boost which is then reduced by throttle body.  The result is a minimum of exhaust back pressure and better efficiency.

The absolute pressure reference aneroid in the controller enables the controller to maintain the MAP setting independent of changes in altitude.

Steve