If you watched any 49er game last year, you probably saw a mistake on special teams at some point. As a result, San Francisco finished 2021 with the third-lowest DVOA in the NFL and was in the negatives in three out of the five kicking units.
The in-game variance will skew the average starting field position as turnovers like a blocked punt or getting stopped on 4th and goal from the 1-yard line. But you'll get a more accurate picture when you look at the metric throughout the season.
The 49ers' average starting field position this season has been from the 28-yard line, which is 14th in the NFL.