Wireless Transfer to NAS Slow Internet

Hello,

I am hoping someone can assist or guide me in the right direction to troubleshoot. I have a Fortigate 60D and FortiAP, and have a 4TB WD My Cloud NAS. When I download and save files direct to the NAS it doesn't kill my 100MB Cox Internet speed. When I transfer files from my iMac that is connected to the network wireless to the NAS the network connection basically almost goes to a complete halt. I checked speedtest and when I normally get 70MBps it drops all the way down to 2Mbps once I am able to get connected to run the test. Users aren't able to stream anything, I need to test to see how a data transfer looks while on the LAN, but was hoping I just misconfigured something. Thank You for any guidance.

Andrew