Not sure if this will help...maybe you got it figured out.  But here it is anyway. 

When you switch to M while the vehicle is in motion it changes the RATE control to manual, and the control valve stays put unless you move it with the + / - switch.  If you switch to M while the vehicle is not moving (completely still) it changes the rate control to manual and also it changes boom control to manual.  In other words, it lets you force the boom valves to open with the master, even if you are in a yellow place on the screen. 

Sometimes stuff gets fouled up and you want to back up and do it again.  Trouble is, ez boom thinks you already sprayed there because it has yellow coverage (even if it was barely peeing) so it won't let the boom valves open.  The way to redo that place is to be stopped when you switch to M and then you can force the boom open.  Make sure you are completely out of the yellow area before you switch it back to R1 or R2 for auto rate control because if you switch back too soon it slams the boom closed again becuase it thinks you've already sprayed there.