Well, I feel a little silly but I have worked out why I was finding them a squeeze - because the booster poppers at the front when I laid her on the nappy I couldn't stretch the elastic fully as the booster was stuck under her bum iyswim
So now I know to pull the booster through a bit and they are a better fit. Have to say, I like it alot without the boosters in the day so can't decide whether to try something else at night.
But while on the subject - I know this has been mentioned before but how long do they take to dry? I washed my nappies on Monday night and hung them all up before going to bed. All the rest I put away this morning but the BB still feel slightly damp around the elastic until this evening. It's amazing.