I am creating a faucet and noticed why some faucets like motherfaucet, moonbitcoin and freebitcoin can pay more to users.

Looks like if you pay to users with the Xapo credit api you can do it via email ( if the user is Xapo user) or address (if user is non-xapo user).
Now Im trying to understand how faucets can pay more if they use Xapo.

Looks like if you pay to a Xapo user there is no fee because it's off blockchain. If you pay a non-Xapo user Xapo returns the miner fee to the faucet owner.

Does this make sense? Can anyone using them say if this is correct?