understanding material blend / mask texture

Hello - i dont understand the below :

layer 2 (green) = Vector param value was override to : (0,1,0,1)
layer 1 (blue) = Vector param value was override to : (-1,2,0,0)

result was as below - the black rectangular in masked input passed the greed of layer 2.
rest used layer 1 (blocked the greed)

note the mask input is a red rectangular - does it matter?

specifically why only when i override it works?