I agree, back when I was throwing more with a swede type throw. It was very comfortable. But, I was more prone to OAT, due to the leverage of the arm, more like a catapult instead of whip. Because I threw with sort of down to up motion, I OATed a lot. Now that I've changed my form, It took me a bit longer to really figure out how to hit it "part of the way." You say you're confused with throwing mids over 300...
I'm throwing putters 320-350', with a Index finger wrapped, fan grip. But, my drivers (SOLF, Cyclones, TL's) are slowly going farther to 380-400', but my last step(stepping too far) and rotation/follow through were hurting me. Since I was stepping too far, it was keeping my weight back and kept me from rotating into my follow through like I should. But, I'm still not getting quite the distance I should be with my drivers, which I personally think is like you say, due to my lack of gripping tighter right at the rip. I have been working with a Powerball to get my grip strength up though. Either way you go, the hit is the most important.