The Ping Test Availability metric is meant to indicate whether the remote host was reachable and responsive to any ping packet during a test run. This means there are two possible outcomes for any individual run: the remote host responds to at least one ping packet and is considered "available" (100% availability) for that run, or the remote host does not respond at all and is considered "unavailable" (0% availabilty) for that run.
Consider a Ping test-run which sends five packets; if even just one of them gets a response then the availability for the run will be 100%. This is to indicate that we were able to reach the destination during the test run, and therefore the host was available, even if it did not respond to all packets. If all five packets time out, then the availability for the run will be dropped to 0%.
So, like Traceroute tests which send multiple packets per hop, each Ping test run will be either successful with 100% Availability or a failure with 0% availability, and there is no concept of "partial" availability for a single Ping test run.
The following screenshot shows the % Ping Packet Loss metric corelated with % Availability. Availability only drops to 0% when packet loss is 100%; all other test runs with zero or partial packet loss have 100% Availability.
