It's not company-approved, it's regulator-approved, which is designed to be sufficient. Airlines have no reason to go above that, except for planning reasons (eg you might want to add some extra fuel to have the option to fly faster on some legs to make up for delays). So I wouldn't expect Ryanair to carry less fuel than other airlines.

The only exception that airlines will sometimes do is to juggle around destination and alternate airports so that they can save some fuel on that (you have to have enough fuel to reach an alternate airport, and then 45 minutes in addition to that).