In my opinion if you don't clean the cills you're only doing half a job. When using WFP you don't need any other gadgets, or even change the angle of the brush, it'll usually come up nice and clean using what part of the brush you can.
Glass, frames, cills, they all get done by us cause it just looks bad if they're not. And it's always the dirty bits that you notice, not the lovely, clean glass!!