Well the short story is that I showed a friend of mine how to setup this solution for himself, and he found a better size box to use. It turns out the 9litre really useful box is the same dimensions but deeper than the 4litre one I was using. This means it has space for all models of differing heights (my Emissary is tallest by far and fits with lots of headroom), and even allows the lid to be magnetised to make use of a second floor space effectively.
I had some spare steel sheet stuff, and the 9litre box only cost me 5 GBP so I replaced my guild storage boxes with this one. I will stick to the smaller box for Neverborn unless I expand that like crazy at some point.
The new box is a little more than double the height of the 'regular' box I use
It also seems to be a a couple of centimetres larger length/width wise
Bonus lid storage
The height of the box allows a pretty generous amount of room above 'regular models'. I've got my Hoffman Crew on the lid here for ease of access whilst i'm taking them in and out to paint :)
Another good option depending how large your collection is, hope this is useful
Thanks for stopping by