The amount of oil in the fork effects what is called the air spring, if I remember correctly. The 'room' left above the oil in the tube. Because you can compress a gas but not a fluid the oil level in the tube does have an effect on the stiffness of the suspension. I'd start with an additional 2oz per leg and then test the ride. If It is soft add an additional 1oz per leg at a time until you like it. I added three inches to a wide glide, four inch tubes w/one inch lowering kit, and if memory serves plus 4oz each did the trick for me.