OK,
I think that most of us have now come to the conclusion that
A. The thrust force acts on the front of the chamber (in a simple rocket).
In a jet pipe it acts on the exhaust unit (which is just behind the rear
turbine), and on the rear face of the rear turbine.
B. The force on the nozzle acts rearwards.
Logically we can say that the resultant forward thrust is A minus B
This suggests that having the nozzle actually reduces the resultant thrust.
Which brings us to the real question.
Why don't we just remove the nozzle and get rid of the rearward acting force?
The above results suggest that this will give us more resultant thrust.
Once again, no heavy maths required (anyone who integrates will be excluded), just imagination and logical thought processes.