The FreeBSD driver [0] uses the same 2G values as for the AR9280 chips.
Using the same values in ath9k results in much better throughput for me.
Before this patch I had a huge amount of packet loss (sometimes up to
40%) and the max transfer speed was somewhere around 5Mbit/s. With this
patch applied I have zero packet loss and ten times the throughput.
My device uses a AR9227 which is the PCI variant of the AR9287.