ATX can be made small form factor. Heck, most of the "mini" ITX small form factor cases on the market are large enough in terms of liters to support ATX.
Auriel is downright tiny, and it isn't like I tried to jam in parts in the most efficient way. If you placed the PSU over the motherboard and eliminated the stand you could have a very sff ATX rig.
But something to think about. To me, usable desk space (footprint) is key. You could "cubize" Auriel, and it would take up less cubic volume, but you would lose MUCH more desk space.
I'm a bit of a footprint nut. These two cases might not be considered SFF by several users on this forum, but I consider them very small form factor for the hardware they support. You can put them on a desk and they are probably have a MUCH smaller footprint than whatever mini itx chassis they are running now. I also design them to minimize CABLE footprint too: