Need advice with intersection of hip and rake

Hi,
This is my 1st roof and 1st post on this excellent forum.
The top pic shows the old shingles where the hip (left) meets the edge of the main slope (rake ?) marked with green line. The main slope is marked w. blue arrows.
The bottom picture shows the whole situation uncovered.

I am planning to install peel and stick on the whole roof even tough the pitch is 4/12. Not paying for labor lets me splurge a bit on materials.

The house is on the coast near San Francisco, we get serious winds and rains from the ocean and fog and drizzle all the time. My lemon tree is covered with moss.

Unless I get additional expert input, I am planning to slide the PNS under that flashing from 2 directions - main slope and the little side roof at 90deg. Overlapping by about a mile. Trim the flashing, replace the little plywood patch and roof over as before.

Please let me know if there is a better way.
Thank you.
Tj

PS: I bought OC Weatherlock and don’t like it at all - not sticky without a heatgun and tears like old roofing felt. After reading some posts here, I am leaning toward Certainteed PNS - Winterguard, 50% more $.