I am not convinced they check duplicate IPs (at least in an automated way to trigger a freeze, perhaps maybe if you were already under investigation). Consider 2 people on Wifi at Panera, splitting their lunch bill - the intended use of their service if there ever was. Same IP. Or they wait until they get back to work to do the transaction. Again same public IP. People went on about using different IP addresses with Amazon payments too, and I've still seen no evidence it matters.
For Venmo you need to worry more about the size of payments you receive and withdraw in a short window of time.