Trying to keep it simple, but also want to do it right...

I'm trimming out mostly awning Windows (Marvin Integrity line). I'm going for a 'modern craftsman' look. Will be using Azek, 1x5 for the top, 1x4 for the sides. All butt joints, with the top piece ~3/4" proud of the side trim pieces.

Seems standard to trim the bottom of a window with a sill that is comprised of two 1x pieces glued together, than milled for a 10-degree bevel.

My question is: I have a fairly large roof overhang, and the windows themselves already have a sill for weeping away water. a 1x trim piece (3/4" true measurement) will sit almost flush with the exterior of the window unit.

Do I need a sill? It'd be great to just install another piece of 1x4 on the bottom, butt-jointed to the side pieces.

Thanks very much for your advice!