FWIW, I was consulting my sleep bible again this evening and the paediatrician was saying that night waking is NOT related to solid food. He says that longer sleep periods are a neurological development. Says that some babies wake one to two times a night for food, until up to around nine months old, after which time they should be able to consume enough calories in a day that hunger does not wake them. The introduction of solids doesn't relate directly to that - apparently.
However, he says that whilst we should feed babies when we know they're hungry (say when it's been four to six hours since last feed); if they wake say, two hours after last feed, then it's most likely a sleep disturbance and going to them just makes the disturbance worse.
He says that if you co-sleep, then babies (and mothers) should be able to feed without the waking being an actual disturbance to sleep, even if it's more frequent than babies who sleep alone. But, that at some point, co-sleeping babies may associate night waking with entertainment or comfort feeding or contact with mum and start waking "deliberately", just in the same way that if you go to (an older - more than about 4 month) baby who is sleeping alone when they don't actually "need" your attention (when wet, dirty or hungry); then they will start to wake more often too.
I suppose you tell the difference by the amount of formula, or the length of time the baby breastfeeds when you go to them at night. If it's a short comfort feed, then you can probably try to drop it.
Also, I was reading again, that babies without a regular nap schedule are overtired at night and so don't sleep properly. I've seen this relate to A that yes, she might sleep heavily where she's not slept enough during the day, but more often; bad sleep during the day means a difficult bedtime and often a waking around an hour after she goes to bed and a late night waking too, because the sleep schedule is disturbed.