FW 5.40 Elevation Plot numbers don't match Basecamp?s

Different sites / services use different algorithms to calculate ascent (think: smoothing). Although I'd expect to see same algo in garmin products I got used to the fact thats hardly a case.
For example trail de trail is a service commonly used to plan ultra races and often serves as a official track source (at least for runs that I do). What happens each and every time is that I end up with more ascent measured by watch or shown in Sporttrack than what was officialy stated. A recent example: official (trace de trail) 4200m of ascent for a race ended up with 5000m (over a 100k course) of ascent according to both Fenix and sporttrack elevation profile.