Attic Ventilation Improvement
The gable vents are short-circuiting the ventilation. The holes appear to be adequate, but as there's a shorter path of less resistance from in the gable vents and out the ridge vents, the holes don't draw very much air. 

I'd temporarily cover the gable vents from the inside and see how things change. Maybe take temperature and humidity readings at intervals before and after doing so. 

Bottom line: It's rarely a good idea to mix gable and ridge venting. 

As to your actual question, you'll need to weigh the cost of achieving 100% of the recommended area vs. 78%. Considering that most standards have some degree of overage built in, 78% is probably adequate, but that's a matter of opinion.