great that he is such a good waker upper!! my LO has always made noises so that i know she is awake, and recently full blown screaming
i think you need to have a better idea of when he wakes up. i mean you should always follow cues and put them down when they are tired but in this case you really have no idea how long his nap was or how long his A time was.
what if you kept his door open and stayed nearby when you though he may be awake just to see what time he is up? or i have known mums to stay in the room for the entire sleep cycle just watching/listening to baby to see when he wakes up.
it may be a good idea to see how long his naps are because if his naps are short and he's awake after just 45 min then you may have to change your routine or approach to try to get him to nap longer. really short A times are no fun either because then you can't get out of the house!