No, the autopetter effect is a 'checkbox' so-to-speak, just being yes there is an autopetter or no there is not and not having any different outcome based on multiple or different location, etc.
No, the autopetter fulfills the petting check (nullifying any potential loss from not petting), and also gives friendship, though half that or normal petting (8 of the manual petting 15). It also gives the full mood as regular petting (32 or 36 mood depending on animal if I recall correctly)