As someone who did uber and lyft, let me tell you that these algorithm are exceptionally fine tuned to meet $/hr over long term driving. In my area, it is tuned to hit close to 20/hr ± 4 dollars/hr. You bet that on some trips uber is taking larger percentage vs other trips to meet this target. This is clearly how their system works to squeeze every dollar out of both drivers and clients.

Note: this is with OR without doing promotions and specials.

Those algorithms will try their best to get you out of profitable areas and stick you with low pay rides once you pass this 20/hr threshold. Especially if you are doing promotions, as they know that you will more than likely meet this target $/hr mark.