Framing basement, if bottom plate is anchored into concrete floor, does the top plate HAVE to be attached?

I am framing my basement, and have attached the top plate to the floor joists, but when I go to attach it in the other direction, it seems we dont have a rim joist that is accessible...it's burried past the masonry wall and it is all covered with insulation....would it be ok to ONLY attach the bottom plate to the masonry floors instead of having it attached at the top AND the bottom...we are using 3 1/4 inch tapcon screws for the bottom plates, will that provide the support we need for standard dry wall? If not...what are some other options? Maybe a brace directly into the concrete wall?