I really like the flavour of yen ben lemons but is there any way of preventing them from having super thick skins/pith?
I picked a few yesterday that were ridiculously large. By the time I cut off the skin/pith they were normal size and perfectly juicy and fine.
Is it just what it is or can I feed them with anything that will help the fruit?

I've had this before, easy to fix. It is a nutrient imbalance.. too much nitrogen or too little phosphorus.. or too much nitrogen causing not enough phosphorus uptake. A good whack of blood and bone will help as while it has additional nitrogen, it is a good source of phosphorus. Do this now and again in spring. This of course won't help for this season, but will going forward. I use a long acting citrus fertiliser, as well as extra blood and bone and sheep pellets around my citrus.

Ahh brilliant thanks Jenna. I will get some blood and bone today.