Off the NW corner of the field. He probably skirts that corner by 50 yards or so. There must be some sort of landscape feature or other reason he bypasses the closer (NW) corner to enter the field in the SW corner. If you can figure out the why you may be able to exploit it to your advantage. Otherwise I'd set up about 50-75 yards in from the NW corner so your wind is blowing into the field.