i think Synthetic underlay (GAF DeckArmor is what I use) is more than appropriate here AND is way better than asphalt saturated granular "ice & water" garbage that everyone uses, to cut costs (by not using Grace. But even grace is not good enough.
Deck Armor is 5 feet of continuous coverage, that DOES NOT trap moisture like most synthetics. And I've been installing roofs in MA for 13 years, and ALWAYS use DeckArmor .. and no rude awakening (just) yet!
The last pic is my own roof - so I put my money in the right places.
I do install metal only though - so a lot fewer nail holes and a much better roof - so no problems that you would normally face with asphalt shingles and ice dams / etc.