I've been thinking further on the topic of getting our nursery-grown plants adapted to the windowsill conditions. And the more I think about it the more I am convinced that, well, size matters. I was instinctively accepting the reduction of size in my plants as a good thing in the past and was actively contributing to it with poor soil and withholding of water. But it wouldn't hurt to contemplate on this matter a bit more.
In the comments of my previous post Bob Stewart and I were elaborating on this while Bob has provided insight and explanation as well as established clear correlation with the light situation on a windowsill that has to be compensated. Please read this when you have time :)
I was thinking about my previous experience with greenhouse-nursery-lithops and could name five instances in which the plants I bought were way too big although probably normal for commercially grown ones. The L. dorotheae and L. aucampiae I got from Mr. Shimada were in fact so huge I had to use two 7cm pots - and they were all one-headed! His L. lesliei were not far behind. Similar situation with the plants from Kakteen Haage. Both growers are not some non-specialized shops - they know these plants and do grow them appropriately. Under their greenhouse conditions however they can feed and stimulate their plants and let them get big because they will get enough light. And light is luxury for us, windowsill growers. In four out of those five instances I had 2 plants of the same species and same previous growing conditions and by now only 1 of each has survived thanks to timely downsizing. Basically, one plant has choked on big old leaves during the first or second regeneration at my place while the other plant has gradually reduced its size and is now doing fine. In those four cases downsizing was essential for survival. In the fifth case both have died leaving me with their babies that are in turn quite small.