Tuning 802.11 systems is an art…
One trick you can try (if your Wi-Fi access point supports it), is to restrict channel bandwidth to 20 MHz, not the full 40 MHz that 11n wants to use.
An AP using a 40 MHz channel (such as for 11n) is combining 2 adjacent 20MHz channels. And to transmit on a 40 MHz channel, you need to have BOTH of those channels clear. If you just use a single 20 MHz channel, you’ve decreased the chances of activity/noise on an adjacent channel keeping you from transmitting.
This can make a big difference in noisy/crowded Wi-Fi environments! Particularly with our little beasties, which aren’t big bandwidth hogs, that’s the good news.
The bad news is that when things get crowded, UDP is the first thing to get dropped on the floor.
So stack the deck in your favour – put your wireless Pi systems on a common 20 MHz wide channel. (If you can’t run wired Ethernet.)