Salumi and chorizo weight loss rate

They probably lost this much because there is some air movement in your basement and the space is larger.
Ovens are good because the space is small and there is no drafts, so moisture stays in. The reason to avoid moisture loss during fermenting is to reduce drying out the outside of the chubs too much, since this can slow down weight loss in drying stage and also the dry outside will not have a chance to ferment.
Basically you do not want your sausage to dry too fast because it may create uneven drying and leave the center of the sausage soft.