I just did mine this week- I've read others' posts on this issue, but I believe the adjustable 'column' you've removed from the tank is spring loaded to adjust itself to any tank shape irregularities (and there are many, given it's a flexible plastic) - also note the three adjustment screws have spacers to ensure they do not crimp the column sleeve, allowing it to self-adjust.
I may be wrong, but this design would allow the the column to bottom itself out in the tank, without you needing to recalibrate anything.
My install this week, as described above, worked fine, providing the full range of guage motion in the cab.