I dabbled quite a bit in the goblin lottery and found out something of great help when trying to get specific outputs (or rather avoid certain ones).

You cannot receive an output of any materia put into the lottery. (i.e. put in 5 different elemental and you only have a chance at 1 elemental output and everything other than.)

Also, putting in grade III materia seems to have an output ratio of about 10% to grade IV. In my experience it is 5% or less for IV > V.

I personally have never seen a lower grade materia output if you have all the same level put in. In about... 1000 materia spent or so (200 attempts) I saw 3 grade V come out. 1 elemental, 1 Craftsmanship, and 1 Crit. Always use the largest variant of materia inputs you can to lower the chance of a bad output and you'll see much more favorable results.