Hmmmm. Are we thinking his pancreas is helping out sometimes or is he just bouncing? He is in regulated numbers which is great. Maybe .5 would give him safer numbers and stop any bouncing.......but .6 does look lovely too, as long as he doesn't drop too low.
How about trying a few cycles at .5 and see what he does. If the numbers aren't as good, try a fat .5 (I know the difference is infinitesimal but he does seem to react to tiny changes )