LamafamaDid a shell check today and with my toes at the front of each boot I have 1.5cm space from the back of the boot to my heal. Technical term, performance-ish I guess.
The best overall description I can give of whats happened is it feels as if the last has increased over the week. At the beginning of the week I could have skied them without the buckles done up (I didn't but you know what I mean). As the week went on my lateral foot retention in the lower boot became non existent. I know what a packed out liner feels like as I put over 60 days on my old boots, this is very different its the botton of the shell expanding not the liner.
Definitely in the right size then. However, if the shell is a bit too wide or too high volume for your foot then the liner will pack out faster since your foot is able to move around more causing the foam to compress. If your fit is a bit snugger, then you typically reduce the speed at which the liner packs out.
Do this next test for me: liner out, foot in shell, heel to the back and then slide forward 4-5mm, shift the inside portion of your foot to the inside portion of the shell, and see how much space is on the outside of your foot. A finger tip is normal, a full finger is too much space. If you have the latter, it could for sure be contributing to the slop you feel.
After this, I would invest into a foam injection liner. No need for a new boot. Just get rid of that excess space with good, solid PU foam.