Just think in terms of the P-V diagram, you want the pressure increase curve to be as vertical as possible to maximize the area enclosed by the cycle
This doesn't help at all. Diagrams are diagrams, what does it actually mean physically?
Think of it as similar to hi compression automobile engine (race car) being more efficient vs a low compression engine (tractor engine). Not exactly correct but a way of starting to think about it
Explosions release more energy in a shorter time, which leads to a higher peak temperature and thus higher kinetic energy in the products. This directly results in more pressure/thrust.