Having trouble using poppy's e

So I've been working on expanding my champion use, and really like this yordle's kit. Tons of fun. But I can't seem to get her e to go off reliable. I don't mean the stun part, i know you have to knock into terrain to get it to happen. But can it not be used in melee range when im auto attacking? that's the majority of the time when I'm trying to use it, and it only seems to activate 1 in 3 times