I use the same method you do... starting 12"-14" from the end of the binding (leaving a tail not stitched) sew all the way around and stop about 12" from the first stitching. Overlap the ends and somewhere near the middle mark the center point on both "tails"...then cut one at the center point and the other 2 1/2" longer than that (or whatever the width of your binding is). Then make a diagonal seam to join, trim press and lay it flat (pin if you need to)...here is where I differ...I turn the quilt over and sew that last 12" with the binding on the BOTTOM! Little tip is "baggie on the bottom" (like "feet on the fold" when embroidering on a pillow case or on the binding with words, etc) baggie bottom allows the feed dogs to ease in any excess fabric, ends up perfectly smooth. This works on the serger as well, when joining two pieces that need to be eased sew larger piece on the bottom!