A lot of it is pelvic bone width... You can only alter it so much. Squats and deadlifts will add muscle, which adds width, so an inch or two around the waist you can definitely do... but I wouldnt guess much more. I have the opposite problem... wide shoulders (thank God) and a wide waist, with naturally thick obliques... so when I go over 12% bf those big obliques' definition gets covered up and all of a sudden look like fat rolls on my side (at least when I look in the mirror! haha), and even when the fat is gone I "widen out" between my ribcage and hips, with the bottom of my ribcage and hips being the narrowest points on my body, and muscle wrapping around my side at the pelvic wings. Id rather have a narrow waist... but I guess the grass is always greener! haha