Yes and no. MM x Val produced several awarded plants with more 30cms size while MM is not known for its big size and Val is smaller than MM.
(Dont' forget too TON use a special method to increase flower size. I think if I buy Tarantula tomorrow, I will never obtain 39cms flower size!)
If TON crossed MM with Tarantula, it's exactly to add Tarantula size to the color and form of MM, what is yet one of the best genetic parent.
Often, we know Big size x big size will produce big size but it's not always this result. Genetic is more complicated and the best results are often from a complementary cross.
In my opinion, it's better to cross 2 plants with different characteristics than to cross big size x big size OR dark color x dark color, etc...