Based on the setting being documented here:
The default value is 20 starting in version 7.0+ (so in all current versions)
That is right about the failover list. If for some reason the client cannot select a desired relay because either the hop count is too high or the network latency in sending and receiving the ICMP packets is too long, then the client will timeout in its attempt to do automatic relay selection and start on the relay failover list in order of the entries listed on the relay failover list setting. This is the setting you will want to use to define multiple relay failover candidates:
You can try to increase the MaximumTTLToPing to 255 and test to see if that will help that endpoint to select its desired relay. You may also want to set this setting and increase it to its maximum as well:
Requires Client Restart: NO
Description: Delay this much between ping groups during relay selection.
This will allow for more time between the ping groups and adding that time increase the total time the listener will remain open waiting for an ICMP packet to come back (good for high latency environments).