[josephrt1]

In California ASA mechanics clinic about 3 or 4 years ago, for base ump starting along 1st base line and ball hit to OF, the instructors were teaching to come inside (traditional inside/outside mechanic) and position 10 ft inside the 2nd baseline and 10 ft off the 1st baseline. That is the 1st inside position. What you do next depends on the play. If the runner rounds 1st and continues to 2nd, you would run parallel to the runner taking them into 2nd base or beyond.
If the player rounded 1st and then had to scurry back on a back-pick, the umpire would move toward the 1st base line to get their calling position, just short of 1st base and 10-12 ft from the base/tag. I don't recall an instructor ever saying to automatically get to the 1st base line. It seems you do need to get inside (the 10/10 position seems pretty good) and then adjust based on where the runner/play takes you.
And of-course, when getting inside you have to be very aware of where the ball is, where the fielders are and avoid getting in the way.