John is a very fine and clever magician. I noticed he does two (2) different color changes from Erdnase. The first is immaculate. The technique on the second one (the one at issue on this thread) is good, but the patter line may invite suspicion. As he places his hand on the top card in preparation to push it forward, he says, "we cover it..." But to a spectator, there is no reason to "cover" the card, so why actually point out that you're doing it?
The motivation (if any is to be offered) for the covering of that top card must be justified. I am far from an expert on the change, but I have worked out patter that suits me and I believe adds the necessary motivation. When I cover the card to be changed with my hand, I playfully ask: "Did you see anything happen?" When they say, "no," I then say, "That's because it didn't happen yet" as I move my hand back, stealing the (second) card in the process, and showing that nothing in fact has happened - that the top card is still there. They always seem to laugh at that line and also to relax. I, of course, am now halfway home, and the change is then made on the offbeat, accompanied by the words, "But just a little wave of the hand...".
In other words, to "change" the card, I like to make a magical waving motion, describing a counterclockwise arc with my hand, as opposed to bringing the hand upward or sliding it backward to reveal the change, which IMHO, are not very magical gestures. I feel that when the change is made, it should look as close to how it would look if you could do real magic. The waving motion has the additional and pragmatic advantage of misdirecting the spectator(s) away from the fact that the hand moved forward just prior to the change.