formself i feel the lower abdomen contract the best during the lowest portion of the sit-up when using one of those decline sit-up bench things. i just stay in the bottom half of the contraction moving up and down with my lower ab contractions...then i move to the top of the motion to better iso my top abs. to really thicken up you "v", i would suggest having a 45 plate on your chest while you do those "bottom of the rep" sit-ups. the abdomen muscles are just like any other muscle, they grow faster when worked out with weights..alot of people only do body weight movements for abs, and do sets with reps from 30-100. could you imagine working out your biceps in such a way, and expecting to see them show up when you flex them? no. same thing with abs...if you want them to pop out, and show up..youve got to make them growoutside of your fat. unless you can diet down to 0 % bofy fat....then you will see them without weight training.
