Thank you The Aziz, I have tried this but its not quite working out the way I hoped, perhaps I am doing it wrong. They don't seem to fit very nicely if I want to then continue more stages after the smaller clustered engines. When I put the largest decoupler it sort of goes in a cone shape upwards and doesn't fit flush with the upper stage. I'm sure they will add bigger engines in the future but for now I may have to rely more on some solid boosters on the sides instead of larger stages underneath.