Yeah the length of the bowden tube can definitely effect retraction. I'm actually fighting a similar problem with my Kossel.

I ended up moving my extruder to the top of my Kossel in effort to shorten up the bowden tube. It improved oozing a bit, but not as much as I would have hoped.

Oozing can also be reduced with lower print temperatures. Maybe try reducing your temp by 5c and try again?

Also, 5mm is standard but I've heard of people using 7mm retractions on a bowden system.