The reason to exclude the 188.8.131.52/28 block from your masquerade rule is to prevent the router from rewriting those addresses (as well as any private IP addresses you currently have and plan to keep using) to your WAN IP.
If you have the rule without the exclusion:
add action=masquerade chain=srcnat out-interface=wan
traffic that goes through your router and out the WAN interface will get rewritten by NAT to look like it's coming from 184.108.40.206 (your WAN IP). With the exclusion, you make sure that any new traffic coming out from one of those IPs maintains its original source address (e.g. 220.127.116.11).
If you don't have any private IP addresses on the "internal" side of your router, then you don't need a src-nat rule at all. Otherwise, since you do need the src-nat rule in order to maintain Internet access for the private IP LAN, you would need to make sure you exclude the new Public Static IPs from the src-nat rule, so they don't get rewritten.