i'm laying a new concrete floor we dug out 9 inches. i had planned to
lay 3" insulation, 4" concrete followed by 2" granolithic screed.
i've since decided against the screed so have an extra 2" to make up.
my first thoughts were to lay an extra 2" insulation, so 2 layers a
75mm layer and a 50mm layer then 4" concrete.

would this be OK... or am i better laying 6" concrete on the existing
3" of insulation.

can you have too much insulation and could there be any movement
causing the concrete to crack?

thanks