Trip Odometer showing more distance than actual

The trip odometer on these units always reports greater distance than actually walked. For example, I hiked 11.8 km yesterday and the Trip Odometer reported a distance of 14.2 km. I have the track log recording track points based on a distance of 0.2 km. Once I view the track on Basecamp, it reports a distance of 14.2 km when I first open the file based on the summary data in the file. I can get the true distance walked by deleting 1 track point to force it to recalculate. Also, despite the track point distance setting, there are still track points logged with less than 20 metres of distance between points. There are 3-4 of these units in my hiking club and they all have the same problem. Is there a way to set up this unit so the Trip Odometer reports the distance walked more accurately in the field?

 

I am using a Garmin GPSMAP 64s unit to track where I went on my hikes in the mountains, the distance and the elevation gain.

I already changed the track point log setting from the factory setting of AUTO, to the DISTANCE setting, with the minimum distance for recording a new track point set to 0000.02 km, or 20 metres. Since the unit is supposed to be accurate to +/- 3 metres, this setting eliminates the logging of most of the erroneous track points caused by the unit's drift while stationary during a lunch break - it only logs a new track point into the track file if it is more than 20 metres away from the last track point that was logged. This cleans up the track file, but I suspect the Trip Odometer doesn't use that same filter and is still recording all the erroneous track points caused by the unit's drift while stationary. Maybe I just need to turn the unit off while I am having lunch?