@new2this,
Network performance is affected by both endpoints, i.e. the AP and the client that you use to test.
They'll end up using the best BOTH of them can handle.
With Wi-Fi, it's a bit more complicated because there are more factors coming into play (distance, obstruction...).
Your EAP620 is probably not the bottleneck.
What kind of client are you using to test?
20Mbps is a practical speed for 802.11a or g endpoint...
With my phone over Wi-Fi, I'm practically getting about a third of my wired speed (when the bottleneck is the ISP), even less the further I move away from the AP.
The phone is the bottleneck (despite support for 802.11ac).
With a laptop over Wi-Fi, I'm back to being throttled by the ISP (although I'm getting close to practical limits of that standard).