I have this issue but the other way, I did a 10m Garmin F5 plus run for example, and Strava auto synced it as 9.93m. Very annoying! It's done that a few times now. I'm inclined to run further just to ensure Strava is happy!
My activities are usually spot on Garmin Connect vs. Strava. Occasionally Strava will be 1/100 mile less.
Strava wants to motivate you to additional 70 yards or whatever that is!
In the past I often had a few more meters when uploading on Strava but in during the last weeks there was almost no difference - maybe a change with one of the latest firmware-updates.
Several threads in the Strava Support site regarding how Strava calculates distance.