How to mass approach in a smart way?

I like to mass approach for example, at events, festivals etc.

One of things I've noticed is that sometimes I approach a girl A and approach a girl B and often times I get one or both girl's number but they will later reject because either of them saw me talking to the other girl.

In order to avoid this scenario, after getting a girl's number, I go to a completely different area to continue my approaches. Are there any better tips? Basically, it seems better to avoid being seen talking to other girls after getting a girl's number.