I was able to measure it quickly: 1100mm is exactly right. One foot is exactly 550mm wide at the top without the "rail". If you push the rail together completely in the middle at the top, you are at 1100mm.

Yes, these masses should be correct. In the explanatory video you can stop at 0:44 (https://www.youtube.com/watch). This middle part can be enlarged and reduced in width and then fixed with screws. If you push it completely into each other, it could come to 1100mm. I have a 1600mm plate and the frame is also much smaller (less wide) than the holes would have allowed, as I have mounted the PC outside the feet at the bottom of the plate.