Hey, sorry to Necro this - But I'm having the same problem; CTRL Clicking adds portions in the multiples of .3 ML's per click and I can't seem to find out how to tune it even further.
Edit: Seems to be based off of what container one is using - Using a Jug sets it to .3 MLs per Shift Click, while a Bottle transfers .1MLs - Figured it out.