Size matters because it has an advantage over smaller fowl. But in "ulutan", you should be wise in choosing your opponent. The longer the legs of the opponent, the harder it is to beat. They have a reach advantage, so size does matter. It is more even in derby because they have a range in weight, which makes the fowls more likely to be the same size.
This is correct. Since the main weapon is attached to the legs, reaching advantage is very important.
Having a big size too means that the fighting cock is really taken care of and treated well with boosters, vitamins, supplements, etc.
However, in most cases, it seems rare to see that in a certain match, we will notice a much big size difference between 2 cocks that will set to fight. There's a category or sort of brackets at this match, of course, to balance everything.