First of all, congratulations on your progress! This has only ever been anecdotal stuff for me, but I have witnessed and experienced this. Someone I know lost a good bit of weight and is now so much more ticklish. I've mostly always been a relatively healthy weight, but for a few years gained some extra due to some medical complications (now resolved). When I dropped back to my normal weight, I noticed I was much more ticklish. And while I have known people of all body fat percentages that are very ticklish, some of the most ticklish people I have met have been on the leaner side. I'm not completely sure why that is, but I have some educated guesses:
There are not just nerve endings in the skin, but also the muscle. When we do soft tickling, the skin picks up a lot of that sensation. If there's enough fat between the skin and the muscle, not a lot of that sensation transfers to the muscle. When we are lean, both the skin and some of the muscle get stimulated more easily. The toner the muscle, the more that sensation may be felt as well. Toned muscle is probably going to keep nerves under a little more pressure or tension, priming them for sensation. I'll add that as we grown more muscle, we tend to grow more sensory and other nerves, potentially making us more ticklish.
For hard tickling, when those deeper nerves are not padded with fat, they can be easily triggered. Fat is very pliable and absorbs some of the pressure, where as pressing on dense lean muscle, it takes all the pressure and sensation directly. Body fat is primarily a storage system for the body, where as muscle has all these complex fibers, nerves, reflex connections, and mechanical functions–They're ticklish!
