This is probably a very silly question but I seem to be struggling to understand levers.

I have floor mounted pedals.
I understand the the closer I attach the master cylinder to the pivot the lighter the pedal will be.
The part I'm struggling with is if I move the master cylinder mount point away from the pivot does it make the clutch more of less sensitive?

It'll make it more sensitive/sharper.

As you move the master cylinder rod attachment away from the pedal pivot and closer to the foot pad there will be less movement of your foot for a given movement of the clutch. So it will be faster for quick gear changes but more difficult to slip the clutch in stop start traffic.