Put simply you never give gold away for free.... and as such a mail order free touch up is no where near an in house dyno derived tune... as one needs to compensate for a myriad of things.
thats why i said (please understand the touched up one is dramatised a bit to make it more obvious) and (ignore the fuel map though as it was to dangerous to rewrite a UK based car with no WB, its cleaned up not rewritten to target afrs from memory)
but your post above is correct, most of our tunes dont have flat af curves and definately have a non linear timing line. Most go up, some go up down up... all the benefits of live tuning.