We are saying the same thing. In normal flow there is no need to stay near the ball because the RFP will probably be blown before they are set. In hurry up you can get in trouble if you do that and the team snaps before the RFP. They are more concerned with getting set than listening for a whistle. It's easier to talk to the center when you are close than 7-10 yards back, especially in that craziness.
I don't think we are saying the same thing. In a non-hurry up offense, fine, you have plenty of time, stay till the RFP or move back a little earlier, it's really not going to matter.
But in a hurry up offense, the U needs to be 7-10 yards off the ball and in position BEFORE the RFP is blown. He shouldn't be anywhere near the ball. He shouldn't be moving AS it's blown, he has to be in position BEFORE it's blown.
Let's look an an extreme example. There are 8/10ths of a second remaining on the stopped clock (yes, I hate clocks that go to tenths in the last minute, but we have them). The offense has to be set for one second before the snap, but there is no requirement for that set to be after the RFP, it can be before. So A comes to the line, sets, and the instant the RFP is blown, they snap the ball. All legal.
But how is the U going to be out of the way and watching his keys to see if they are set if he is staying with, or even near the ball until the RFP? He HAS to be away AND IN POSITION well before the RFP is blown.
Even in the less extreme hurry-up offense, the ball can be snapped the instant the RFP is blown. If the U is staying "near" the ball to tell the snapper to wait for the whistle, he's going to get run over as soon as that RFP is blown.
If a team is in a hurry up, set the ball, and get set in your position BEFORE the RFP. If that means you have to be 7-10 yards away when you tell them to wait for the whistle, then fine, either tell them from there, or don't tell them at all. If they don't know to wait, they probably shouldn't be running a hurry up offense. Telling them to wait for the whistle is a courtesy, not a requirement.