just been doing a bit more lemoncello research and came across this, Have never seen this stated before it could be worth a try........
"It’s important that the lemons are just ripe, or even still a little green, because that’s when the skins have the highest level of oils and will make the most flavorful limoncello."
Link below to the page this came from
http://www.charmingitaly.com/limoncello-campania/There could be something to this as Im begining to think that the best batch I ever made was made with lemons that were "just ripe"