A working trot is a working trot is a working trot. Rising or sitting, in a corner, on a longside, on a circle, in a leg yeild and yes, even on the diagonal. There is one working trot for all of these things and yes maura is correct, it must stay the same throughout the whole test for maximum marks.
The reason you may be feeling that the judge likes to see more trot on the diagonal is because the judge probably wants to see more trot everywhere in the test, not just on the diagonal. A good working trot has quite a bit of thrust from the hindlegs.
They say money doesn't buy happiness -- well happiness doesn't buy horses!