While it does create a queue in Y. Most F pax remain seated until they see another pax exit the lav and it does avoid congestion. In Y it's congested do to the number of pax in a small space. Many aren't waiting for the lav, they just want to stand for a bit and stretch. One of the only times I allow Y pax to use the F lav is if the cart in the aisle and none of the F pax are waiting for it.