I've been racking my brains on this saddle thing, there was something in the back of my brain nagging.
Many of the cool pads I've been looking at have 'husk' type spacer material in, which I was using for the last few years to keep her back cooler since she had that haematoma in 2014, and the reason I chose the le meiux pro sport 3D pad as it has it built in, but after it left the imprint on her back in December I didn't use it again.
I've just sat going back through pictures looking at my padding because at some point this year I stopped using the spacer material, low and behold I didn't use it on our beach ride on 25th May and used the le meiux on the 26th because I told myself I'd been silly about it. The first problem was noticed on 3rd June. I don't think I put the spacer pad back on in that week and didn't after the saddlers looked at her because I didn't want to change anything and the advice was to just use a cotton pad.
Perhaps it is a heat issue after all and I'd already found a way to mitigate it but just forgot the importance of it I suspect it had minimised the impact of the flat flocking too. She is the princess and the pea, one tiny thing can make all the difference to her, 99% good isn't good enough.