[QUESTION] Lowering string tension sound better?

Hi guys,

so I started learning cliffs of dover a few week ago and got the intro down, the problem here is I cannot play it cleanly when I start to increase the speed so I just start practicing more. One afternoon I change my tuning to half step down to play another song and when I tried to do the cliffs of dover intro run, it sound noticeably better and I have no idea why. I suspect it has something to do with the lower tension of the string that allow me to press the note clean. Does any one have ideas on how to improve when I change my tuning back to standard?