No, i don't think you were taught modals in a wrong way. I guess it also depends on the author they base their theory to support that. I studied modals with Alexander and also Quirk. According to what i remember and i was taught, the scale is:
might
may
could
can
should
will/would
must
to be
but hey, i could be wrong.. i'll try to get some websites for you later on..
Cheers
Rootless tree