NXC2500 Wireless Internet Speed Slow

Hi,

We have a NXC2500 and several NWA 5121-NI access points.

We have set up as per these instructions:

https://static.spiceworks.com/attachments/post/0016/7487/Setting_Up_and_Configuring_the_ZyXel_NXC2500.docx

Basically, two separate networks, one “Office” one and one for “Guests”

The issue is the actual internet speed is barely reaching 20MB, despite us having a 200MB leased line.

But, most devices are connecting wirelessly at around 70MB+,  ok I don’t expect 144MB but surely it should be faster than 20MB?

ie:

I have played around with Wireless Channels to no avail, and changed the AP SSIDS to no security to rule that out.

Also if you plug a laptop in directly to the HP POE Switch, it achieves speeds that match our internet connection.

Does anyone have any ideas?

Diagram of our setup below: