FortiAP Client Load

I have 4 U433F AP's in a gym. 2 of the AP's handle most of the load. I turned on AP handoff when client levels reach 35 clients. It doesn't appear to be working. We are only running Dual 5 Ghz with 20MHz channel width. We are on FortiOS 6.4.2 and FortiAP v6.0 build0080. We have another gym with the same issues.