Why still no dive acceleration difference?

[Crumpp]

CSP could maintain constant efficiency roughly when speed of propeller tip is below 0.85. Please check 3-blades efficiency curve, when advance ratio is far greater than 2.2, namely when prop tip is approaching 1 Mach, the story changes. A CSP will lose efficiency inevitably at high speed diving(a/c noise louder and louder).

Btw, CSP will also lose efficiency when TAS is very very low.

You are correct but don't misapply it as it has little bearing on the game shapes in IL2.

The efficiency is nearly constant in any portion of the envelope that design can sustain flight....

That is the beauty of a CSP.

The very nature of power producers is such that the faster they go, the less thrust they produce. The reverse is also a characteristics of power producers. The lower the velocity, the more thrust they produce. That efficiency drop occurs because the propeller blades are stalled just like in very high speed flight. The reason is different but believe me, both realms, high and low speed, produce stalled blade portions. In the low speed realm, we are looking at speeds at taxi and the first part of take off but our thrust force is extremely high at low velocity. Therefore, in the scheme of things, it is a useless detail to include the reduction in efficiency in a dive. The performance is not sustainable in the first place and our reduction in thrust with velocity is already well approximated by:

Crumpp says:
Take the force triangle for a dive. A component of weight contributes to thrust based on the angle of dive. The difference between the force on the axis of motion in the dive and the force on the axis of motion for level flight is your initial excess force that will move the aircraft to its new equilibrium point velocity. The derivative between that and equilibrium is your average excess force along that vector....

In other words, the details are included when you make the standard assumption of .85 efficiency.
You could also incorrectly conclude that all subsonic propeller theory violates the very definition of lift because it does not include the fact lift force develops at right angles to the relative wind. This means that in all propellers, regardless of blade stalling will not produce thrust. Why? As the velocity increases the relative wind gradually shifts and eventually lift produced by our propeller no longer parallels the flight path but is deflected upward.
Fortunately we don't have to do that or at least we would not be adding any accuracy by deriving our own approximation of the effect. It is one more thing rolled up in our standard formulation.