I heard that one of the substantial differences between a tonal composer and a modal one lies precisely in the fact that, starting from a common scale, the former considers it primarily for ascending motion and the latter for descending motion.
This type of approach, mindset, guides musicality differently in moments such as cadences, etc.
The categories "modal composer" and "tonal composer" are already a bit strange, anyway... let's say that Palestrina is an example of a modal composer: well, his melodic lines are neither more descending nor more ascending than those of Bach, nor those of Boulez.
Furthermore, what does it mean that they start from a common scale?
(If instead you were talking about modal jazz, I don't know much about it, so just ignore what I said!)