#Define how much XP will be drained from player when flying by wearing classic Angel Ring? Put 0 if you need to disable XP requirement for flight.
#Range: > 0
XPCost = 0

Angel Ring continues to drain XP if set to 0 as shown above.

Perhaps due to the range being set to > 0 and not ≥ so 0 is included? Random guess. :)

Seems you're using Angel Ring 2.0.0, as of 2.0.1 it uses it's own server config file which can be found in each world save in your modpack. Change the XPCost in angelring-server.toml to switch to Classic Mode.