Top of divider is 3ft, bottom is 2ft. No need to be angle, minis have heaps of room in a side load.
Larger mini ponies/small shetties like mine, I have my bays 2ft wide, but mini horse can get away with 18 inch (my filly will actually fit in that too & she's a big girl), so in a standard double float, you can fit 4 mini horses easily behind the original chestbar & another 1 or 2 up front.
I've designed mine to carry 3 so they have plenty of room... But can still carry another up front if need be.
Dividers are padded... I prefer not to have rubber on them as it makes it harder for ponies to spread their legs (for stability while travelling), specially if you go for the smaller bays.