Thank you for the update. I've been tinkering with my test scene for a few hours now, and I can't get this to work as expected. Here's an assembled screenshot of the results of two different label sizes:

Each time I execute the Envelope Content script, the Transform that it's attached to acquires either a positive or negative X value, despite being initially set to 0. The Content Root Transform inherits the same X value, despite being anchored to the left and right of Envelope Content. If I repeatedly execute the script with the scene running, Envelope Content creeps a little more to the left or right. In addition, the children of Content Root (Icon and Label) are also offset visually, despite their transforms showing as 0.
Can what I want be achieved without any additional code, or do I need a custom script in the scene to reposition the content? I'm an artist, not a programmer, and I'm trying to get this to work without having to get the code team involved if I can. I assume I'm just doing something silly, but I've exhausted all the permutations of anchors/pivots etc. that I can think of.