It may not seem that much could get under a properly scribed ridge cap BUT
I was in a roof last week with a prety well scribed ridge and alll the way down the middle of the cieling was a thick scatering of fine vegitable debris.
Not whole gum leaves as such bit little bets of fibre from the flowers, eucalipt caps, tiny bits of twig and little leaves like from a leopard or poinciana tree.
This would have been at least 22.5deg pitch.
Over a long period this accumulation can get quite substantial. I have seen this in a number of cielings over the years. Tile rooves with no sarking can be realy filty places if there are trees with fine folage near by.
cheers