Bet size for a bluff in this spot

This is the spot: you have AK or AQ or maybe AJ or KQ, and raise. You have one caller to go to the flop.
Without connecting to the flop, you C-bet nonetheless because it’s a dry flop and you have two over cards.
The turn is another blank, you check and opponent bets small, you call with two over cards and still a relatively dry board.
The river is a high card, but it doesn’t give you a pair, like you had AQ and the river is a K, or if you had KQ, the river is an A. Perfectly representing your range for a river bet, on many occasions you actually do have the best hand.
So you have basically A high with no pair, how much would you bet on the river to bluff the opponent of the second or third pair?
From my experience, half pot bet size works, but lately I’m thinking 2/3 or even pot size is better.

Thoughts?

edit: you are OOP