I found that (H+L+C)/3 gives annual returns between C and (H+L)/2, with a multi asset strategy with 4 hour bars:
(H+L)/2 - 252%, error 14%
(H+L+C)/3 - 234%, error 17%
C - 221%, error 20%
So all are pretty close, but I only have this strategy so far. I'd be interested in results with different strategies.