Ok I'm back now!
Looking at your routine I still think a push in the morning A times might help - it's quite usual for LOs to be able to fall asleep easily at an A time they're used to, but which is still not quite long enough to enable them to have a nice long nap. Some LOs need pushing very very gently, taking lots of care not to let them get wound up - my DS only ever managed a push of 5mins at a time! But others seem to take it in their stride, you may well have a good feel for what yours can handle, so go with that, but do try a little push. It may well be that 2h 15mins is still right for him later in the day, especially after a short nap or two - that would be quite normal to reduce A times as tiredness accrues during the day.
Now as for BT, I think you're right that he's tired enough to sleep then but hasn't quite accrued enough A time during the day to be ready for night sleep, if that makes sense? So on those grounds I'd also be suggesting a push in A times, which could help with that if it works... And then maybe as you say, pushing BT a little later too, but that will depend a little on how much A time he's had during the day. It's a bit hard to judge but looking at what you've posted so far, it seems he needs at least 9h A time during the day, perhaps a bit more? Time spent resettling or feeding to sleep you may want to count as worth half of the A time when he's properly up, so you could consider that when working it out. You may not find that useful, I just mention it as I find it useful personally to have an idea of how much A time my LOs need over 24h (or conversely how much S time they need!), as this is likely to stay fairly consistent over a long period of time, whereas A times and naps etc will change rapidly, as I'm sure you've already experienced!
Poor thing though with the tummy bug and all that
IME those multiple wakings at night with lots of crying often have meant discomfort of some sort - I suspect the reflux, it could of course be teething and/or the stomach bug too, actually reflux tends to flare up with teething as well
Does that make sense? Sorry I feel I'm rambling