Column width in back office order overview

[NSN]

I have insert the tracking number in the order list in the back office. I did it by following vekias guide https://mypresta.eu/en/art/developer/tracking-number-orders-list.html

All works well, but as I sometimes have quite long tracking codes, I would like to set a fixed width for that column. Otherwise it get a bit inconvenient to use the order list as you can see in the attached screen shot.

Does anyone have a clue how to either set a fixed width for that column or any other idea?

Shop runs on PS 1.6