The shingles rest on top of the drip cap like this or you can install the under shingle on top of the little raised area and then the top shingle like what is shown in the photo. I installed both shingles in front of the raised area because that is how the original drip cap was installed on this house. 6 of one half dozen of another.
I needed maybe 8...10 at the most. So I bought a small package of fender washers at 6 pieces for 98 cents. I sprung for two packages and made my own .
Here is the after drip cap install but before shingle install. Not only does the drip cap serve a preventive purpose but it also adds just a tiny bit more of detail to the window trim. Which reminds me that..... The devil is in the details
Devil is in the details
Notice the insulation installed above the window in the photo above.