I overlooked the fact it was set to points, not pixels. I always thought it was much of a muchness as I needed to export at a variety of sizes anyway, and was planning to control this in export. My main concern now is realigning my existing project of over 100 icons, so that the slices are created in export at the actual artboard dimensions. I'm really at a loss so help would be appreciated.
There is an issue (bug?) which means vector shapes are not exported properly at low point resolutions. Eg some curves in my 8x8 artboards were being twisted. Options like expand stroke also do not result in smooth 1:1 curves. Unfortunately I was not aware of this issue as I was exporting test icons as PNG (which were fine).
To get realignment, I think I may be able to resize the entire document by 0.9 (bringing 4.444 back to 4.000) or there about, however the document setup is not allowing me to alter the entire document values (I was hoping I could resize the whole thing). If I select all, I'm only selecting contents, not artboards. I can't simultaneously select and resize artboards and contents, and doing them separately results in shapes connected to the wrong artboards.