Regular jelqs mostly hit your side chambers (cc's), while V's mostly hit your bottom chamber (cs). They both hit all three, but each hits one more than the other.
7", is this happening from the get go, or as you move more into your routine? If you get good V's in the beginning, do fewer V's and more sets. Alternate between regulars and V's. Make sure to really bury your unit into the webbing of your fingers, you have more strength there, and bend your wrist upward as you apply initial pressure. Not to take anything for granted, make sure also you are using your index and middle finger. You might just have weaker than normal finger strength, and if that is the case not sure what you can do. If in fact V's aren't going to work out for you, make sure you move your grip around while doing regulars.