Mine are all 'layers' too Lindy, I think it is a case of some do and some dont! Mind you I also think that a big, bouncy, deep bed can help, especially when a very pregnant mare can 'sink' her over large tummy into it when she goes to lay down. I'm suprised that Maxime didn't/doesn't lay down more, coz I know from your pics that she had plenty of lovely bedding!
Suzie doesn't look too comfortable, or she didn't a few moments ago - lots of heavy breathing. Then she laid flat out for a short while, now she's up again, but having a grazing stint. Think it a bit strange that she didn't stay down for very long - not like our Suzie?