I better rephrase that. I meant relative to the low pitched prop.
As speed increases, the effective angle of attack is reduced, and so is the engine load of course.

@ Yallaair
Prop stalling is of no importance here as long as the effective blade angle is smaller than 25 degrees at 75%D. Note the word effective, which means after correcting for diameter pitch twist. Below this angle, the prop operates with the airfoil lift curve in the linear part. When a prop approaches square values like 20x20, the prop thrust will no longer be linear, and rotational drag will increase. This is not yet stalled! Stall sets in when at the same rotational speed, the thrust values decrease with increased pitch.