Mum', I think you're going to find that part of that frustrating "everyone is different" thing about CH is that there are many ways in which cycles develop and end, and they don't always stay the same for individuals from one cycle to the next. I would guess that the most common pattern is ramping up pretty bad in the days before they fade away. For sure, it would not be unusual for the D3 to now be having an effect on his attacks.
I have questions, one of which is more appropriate for a closed board such as "Share Your Busting Stories." Does he still not have access to oxygen when he gets his attacks? Is he doing anything to abort his attacks? Is he doing anything besides D3 as a preventive? And (the closed board one) is he busting now? All of those things are going to affect the pattern of his attacks, and maybe the duration of his cycle.