I had this exact same observation. Guessing that the 2x2 calibration is fairly rough like Bar mentioned. Still, for people where calibration will eventually succeed, it’s probably a better starting point that’ll reduce the need to tend belts. Maybe after this rough calibration, the machine gives 10% extra slack than the calculated length on the belts instead of as-needed slack.
I also ran a full 10x9 calibration on 1000x700mm after and that failed, so this isn’t yet the panacea I hoped it would be 
(at least for my setup). I’m going to try doing some more simulation and throwing out points to see if that helps.