We solved this by basing competitions on time, not miles.
After 1 year of using TR, I found a swith in the Wahoo app
(in english probably something like “ERG mode Speed simulation”)
this was off, resulting in 1 hour 200+ watt TR session in the small ring to 20 km on Strava, with this setting enabled, I get 30-35km per hour on Strava, but my garmin still does it’s own thing with the distance, But the TR → strava route is more realistic.
(I do this -only- for strava followers that have no idea what 200-250 watt for 60 minutes means 
)