You are correct, Witness rewards are not factored in, but we only have just over 100 witnesses that get rewards and those rewards drop off sharply after top 20 and after that to insignificant levels after the top 60 or so.
There are probably even fewer of DHF recipients to worry about. In total we are talking about less than 100 Hive accounts that can be significantly impacted by those two exceptions and it would apply to all other hivers 😀
If you are moving HP around that is a zero sum game, you can't improve KE score in both places/accounts...
So I still think that for the mere mortals the only real way to manipulate their KE is to buy and stake Hive.