360 stalls on deceleration from throttle blip

My 340 ran 200K on ported vacuum. Ran great too. After rebuilding it and going with Eddy heads I couldn't get rid of my hesitation. Jetting, checking transfer slots, Recurving the Dizzy. Just went to manifold vacuum and wow what a difference. Now I just have to do some light fine tuning.
Why do you think mine runs so much better on the ported side of the carb while yours got better on manifold side? Different distributors? I just hear so many different things from people on this. I’m just glad mine is finally running better but I do want to learn the science of it all!