Here's my rule of thumb. Adjust the height high enough to get that "PERFECT" grip when withdrawing your xdsc, regardless of how much kydex is exposed. Make sure the pistol is not to high where there is too much space between your grip and the top for your belt. And of course not to low where you cannot grab and withdraw your pistol in a timely manner. Especially in a high stressful situation.
I've seen pictures where the pistol is buried so far down that my guess is that the person would not be able to acheive a solid grip while performing a fast draw. As we all know, in a highly stress situation, EVERY SECOND COUNTS!
Besides, why have an adjustable height/cant holster if you won't adjust it with precision based on the size of your hands, type of pistol etc.
Your xdsc in a MTAC holster is a great choice for concealed carry.
BTW as far as I know, there are no safety issues based on the height of your pistol.