Fizz on hit not proc-ing

I started playing a lot of Fizz recently and I've notice that when I'm using his Q to combine with sheen etc. if I am standing too close to my target, usually almost on top of them, the sheen won't proc on the target, this has messed up my farm some when I'm trying to farm under tower and my damage is a bit short, I would Q to get the proc and get it, but sometimes it doesn't proc and I lose the farm. I am not positive how close is too close for the bug, but it seems to be roughly a minion's width away or so. It is a little frustrating when the tooltip says it procs on hit effects, which it does, just not with the above bug. Resolving this soon would be a great relief, thanks! wrestleolympians*[slayer-jinx-catface]*