Main output volume differences and monitor sound difference

Hi - trying to sort out routing for live gigs.

I noticed today that there is about a 6-8 db difference between the xlr main output and the corresponding 1/4 main outputs (1/4 is quieter). Am i missing something here? is this the +4, -10 difference between xlr and 1/4"?

Also - when comparing the monitor output signal with the main out the monitor was was smaller and quieter as well.

I am hoping someone here might be able to point me in the right direction..

Many thanks

I had know idea after all these years - appreciated!