I would just tile up to bottom of window so as not to detract from window. There's a lot going on there with the mountain bars and the fact that it is a bay window. Having said that, my husband tiled an awkward angled wall in our kitchen and he cut the tiles such that some of them appeared to be a full tile wrapping around the curve, ie. he didn't grout between them and we tried to match tiles so they would appear as one. It looks good, but it was a pain and its in a low visibility spot. Elsewhere in the kitchen, I would tile from countertop up to bottom of uppers and then use Schleuter strip to finish vertical lines at edge of windows ( I hope that makes sense).