What I noticed, and also others in this
thread is that setting the camera to manual discharge allows the flash to fire at full power.
But, if you use wireless mode, then 1/2 power works only partially, and full power does't work at any shutter speeds.
I tried testing slower shutter speeds at full power, and each time, my exposure didn't catch the flash.
Servo mode is essentially dummy mode, so I'm theorizing that in wireless mode, the initial pre-flash is triggering the speedlight before my shutter opens. Though, by the T values, I would surely be more likely to hit full power than 1/4, unless the flash delays firing at lower powers since the T values are shorter