Class 1 deferment

Hi

A client has 3 employments, lets call them A, B and C.

The salary for A is £22,000, for B £30,000 and for C £6,000.

I applied for class 1 deferment and was hoping to get this for employments B and C.    I was unsure if B would get it due to the amount straddling the threshold of £42,475 and, as suspected, they haven't granted it but I don't really know why.  Is it because it straddles the limit or am I just making this up in my head?!

Only C obtained a deferment.
Can anyone provide me with a quick reason as to why the outcome is the way it is?

Thanks