I think that will depend on the wifi driver (on the tx side), and whether or not it's not sending 802.11n/ac aggregate frames immediately (and how long it's waiting). Some drivers will buffer up packets for some period of time before sending them out. So on a lightly loading transmitter, in a quiet RF airspace, the driver might add more latency than is necessary.
One thing I've seen is that the wifi aggregates, because they are so large (64KB), can end up creating some odd RTT sawtooth patterns as a full aggregate will contain packets with many send times, all received at once.
-Aaron