Flights Climbed Recorded By iPhone/Apple Watch Seem Too Low

I have been trying to track my elevation gain (recorded as "Flights Climbed") on my iPhone and Apple Watch, but the daily totals I see in my fitness app seem way too low. For example, yesterday I did a hike with ~350ft elevation gain (recorded with gps app), but the fitness app says I climbed 5 flights. I thought a flight climbed was defined as ~10ft of elevation gain.