That's the beauty of the SC/TO; things happen in a relatively slow and even progression, and there's not much that can go wrong. You'll notice that with the larger bean mass it takes more to get it moving, but you'll also notice that once they do get going they like to keep going. With that in mind, try to anticipate 1st crack and avoid pouring too much heat into the beans. While you don't want to stall the roast, it'll be easier to detect the end of 1st and control what happens after.