This is how it works. D is auto, the gears will change up as soon as possible for economy on light acceleration. If you do floor it, the gearbox reacts and extends the rev range and it will drop down the cogs to find power it all depends on your throttle usage. Sport will try and KEEP the gear and revs at the optimal power output so you have the optimal ability to go at any time, it will also blip the throttle between gear changes on down shifts. Sports mode is all about optimal power as much of the time and is full auto mode. If in D you pull the gear selector towards you it will let you control changes with the paddles or alternaitvely you can just use a pddle to override and you will automatically be in control. The gearbox will prevent you from under and over revving still to preserve the engine.
The car is very clever and the DSG gearbox and engine work in tandem and respond to your driving style.
ED