I have always considered it important that the holster stay behind. Should you need to draw it when it's real, you would want it fully capable of firing and cycling - something with which the holster may interfere. If you determine that your gun needs to be drawn - presumably you may need it in that very instant!
And, as always, you WILL act as you have practiced - every time. This has been shown many, many times. I have read reports about some police officers, some years ago, trained with revolvers and were taught to empty their spent brass into their hands and put them in their pockets to save from cleaning up after practice - and then in real shoot-outs officers were found to have pockets full of brass after the event. In some cases the delays incurred in collecting the brass led to injury and even death.
The point is - practice means something, do it right and when it counts you will be on 'auto-pilot' and do almost everything as you practiced. Most people in high-stress events report that they 'didn't even have time to think - "I just reacted".
