I see but I remember a lot of your posts in which he was having long stretches of 10-10.5 h nights... So that 11-11.5 h were alternating with shorter nights. So it is not that 11.5 h was the rule. I agree that 9.5 h is less than 10-10.5 but you are shifting his body clock, and this can give some ew. And this is following two very long nights anyway.
How is his activity level during the day? My ds needs a LOT of running, jumping, walking, playing with the body, so that he needs to be outside a lot (or doing some actuvity at school or after school) to be proper tired. I don't think I could provide this level in other ways...