I used to do the same thing. I would tell my girl... oh! the regulars are too small and buy magnum twisters. Anybody can fit in a magnum, anybody can fit in a regular. I realized after time, you want the tightest fit possible... it feels better. If you dont like it tight ur either trying to impress somebody, or you dont like sex. think about it pleasure comes from friction, friction comes from a tight fit... that can be in the form of condoms or vaginas.
have you never filled a regular condom up with water? have you seen how big it gets? I could wear one as a pant leg.
magnums are a marketing scheme to help guys impress their girl friends.