> My friend claimed betting at the same TC when 2D left
> versus 4D left at 6d shoe should be different. Was he
> correct? For example, if I bet $500 at TC 4, should I
> bet less if running count 16 with 4D left than when
> running count is 8 with 2D left?

No, the difference could and would be noticed at deeper penetration levels but not with two or four decks left. This is called "floating advantage" and Don covered all of it in his remarquable "Blackjack Attack 3". You friend would be correct if you could play at penetration levels over 5/6.