I was just told that currently ShipStation only supports 4x6" labels or 8.5x11" labels, but we have a new shipping box that we need a smaller label for (max of 4" x 5 1/2") and won't be able to do that. Luckily we can make the 4x6" work, it just looks a little bit silly, but if multiple label sizes were available in the future that would be great!
I have the same problem! Aside from these labels being too large for the packages I need to put them on, only two per sheet is EXPENSIVE. I can't understand why "parent company" Stamps.com offers a 4-label/8-1/2x11 sheet and ShipStation does not. My only suggestion, Staghead Designs, would be to print your label out on paper and then photocopy it in a % smaller that will give you the smaller size you need. I haven't tried this yet; I don't know if you can shrink it down and make it fit correctly on one of the four-up label sheets. Of course this is a huge lot of work, i.e., likely to destroy any kind of profit margin.