Stop with the theory!
The idea of the large outlet is to make the job simple
More air can flow out of a larger hole
unless air flow is happening there - (you already know this )--no air flows in at front.
You DO want low pressure at outlet -
Make a lip in front of outlet - disturb the air at the lip and low pressure happens just above -in the hole
Cowl flaps on full scale , function in exactly this manner .