When dealing with multiple browser windows for rearrangements all windows are doomed to use the same zoom level.
This is a bit tedious when dealing with one huge and one small rack.
As far as i know the browser zoom level is always the same for each (sub)domain.

@modulargrid can you try to add a 2nd subdomain which serves the same site (like www2.modulargrid.net ) to allow different zoom levels?
Or will this break the copy paste functionality?
In case you give it a try dont forget to set canonical meta tags and disable site indexing.
thx!