This is how you shorten your jeans while keeping the original hem! A great trick to reattaching the hem will keep your jeans from looking unfinished: http://www.ehow.com/how_2305591_reattach-original-jeans-hem.html?utm_source=pinterest.com&utm_medium=referral&utm_content=inline&utm_campaign=fanpage
the center back crotch is tipped outward to make room for the rear. How much it should tip depends upon how much rear we have. If your rear is more flat than the standard then your pattern should tip less. If your rear is larger, then your pattern should be tipped more to make enough space. The green lines roughly represent those differences.