Eric, were you using this feeding schedule back on 4/19 and 4/21 when the fast drops happened? I think this is a good feeding schedule, but you might need to increase the food at one of the earlier times just before you know he tends to drop fast.
I am not 100% sure, but when you saw the big drop on 4/19 it might be possible that there was still a residual of the .75 depot left for that cycle.
With these fast deep drops he could just be bouncing. As I understand it if they drop more than 50 points in an hour that can cause a bounce, and even at these smaller doses he could still be bouncing from fast drops even if he isn't going to green, but with out more mid cycle tests it is hard to say for sure.