said by silvercat:....As you know, what could also cause congestion is having too many close neighbours using the 2.4 Ghz wireless network.
Good catch !
So if direct works better (or do it anyway) maybe try setting your WiFi to use a different channel ?
6 is default on most routers, so adjust router to try 3 or 9, or even further away from 6 than that.
Even better, if you do a 'site survey' with one of the computers (or sometimes can do this from the router itself), it may tell you what other WiFi networks are nearby and which channels they are using, so that you can avoid them as much as possible.