Hey man, I might be able to help with this. First off I am sure it is pretty normal to see this happen. I have talked to quite a few others that have the same problem, including myself. This is what I have been doing.
What I like to do is get to about 70% erect and grasp as far back on the shaft as I can. Then I kegal in the blood to get full expansion of the shaft from blood flow. You may have to release at the base just a little to let the blood get in. Be careful, don’t over fill to much watch the head as it starts to balloon as well. You might notice lots of tiny bumps forming at the head and the blood will also darken the head and shaft.
Now once the shaft is almost full balloon I grasp hard at the bottom so that the blood cannot back flow, this is important as I have read it is not good for you to allow the back flow, it could cause injury. Then I grab at the head and slowly push back toward the base. Do this carefully, the goal is to fill to the bottom. good luck.