Check out www.airvent.com, you will find formulas to determine what the necessary ventilation would be for this home. I am concerned about your statement that there are 2 turbines and 2 gable end vents, this is not a very balanced system and is prone to short circuiting. I too am curious about the dormer, is the space the dormer serves a finished space or open attic? If it is finished then I ask how is the attic ventilation system you detailed supposed to serve the area. If it is unfinished then you likely have a dead air problem, the air is entering the gable end vent and going straight out the nearest turbine.
The ideal attic/roof ventilation system will wash the underside of the roof from eave to peak with cool air, just as rain water flows the opposite direction on the top side of the roof.
Look at air as a lazy entity, it seeks the easiest path to get back out of the attic once it comes into the attic through its inlet area. However the air that is just sitting around in places here and there is likely to continue to do so.
Be wary of obstructions that may be in the attics that can block the flow of air in an attic. I have experienced situations where the boxes of ‘sh…tuff’ was piled so high the attic could not vent correctly.
Look closely too at the flashing at the bottom corner of the dormer, I would have fired an employee that installed this way. The method used allows for a direct entry point for water providing that there is not any other flashing that is out of site under the shingles (I doubt that there is), this is a common mistake made by people that install roofing and siding and the reason for most of the leaks I repair at the corners of dormers and chimneys.