Question about connection Microsoft Teams behind Firewall NAT device use Single IP Address

We have make some network setup like below

1.Our original path to internet : LAN (Internal Network)->FortiGate->WAN Load Balance(Ascenlink)-> 2 ISP Internet Access (for Load Balance and Line Backup)
2.at FortiGate Policy. We create a new Poicy , setting is . Source (Internal Network) -> Destination , Internet Service DB( ISDB) pickup Microsoft_Skype_Teams) , and no SSL Inspection and any UTM Security Profile check. NAT can use 1 IP or 5 IP (IP Pools) configure
3.We use another ISP Line(100/40Mbps) and setup a Policy Route UDP Port 3478-3481 , route to the new created Policy (for Microsoft Teams)
This Policy can make sure Microsoft Teams service access internet don't passthough WAN Load Balance

This moring we have a 47 user conference call, Some WFH and Some at Office ,The meeting host use Desktop Sharing to show his screen (one to many). The finding is:

1.When meeting start . we observe user count over 20 users into the meeting room. We use the RTQ function to monitor my Teams client
We can see The Application sharing detail (inbound) start to grow rapidly to Packet Loss (14%)
Then we change NAT config from 1 IP to 5 IP Pools Config. The Packet Loss will to decrease obvious (about below 0.5%)
2.The line MRTG bandwitdh show 5 Minus average is 20Mbps(Inbound)
3.This configure . Our Desktop Share screen lag will decrease to 1-2 Sec. The original config will be 5-9 Sec.

Very intresting. When the packet loss start to increase obvious. We change NAT use 1 IP change to use 5 IP Pools . It will start to decrease....

sharing the result to people like us.