I assume when you say that you are only pinning your quads, you mean you are pinning different parts of the quads? I have 3 different places on my quads to pin. That isn't including my tear drops. Are you rotating between these spots?
To answer your question it isn't your muscle that absorbs the oil. It is your bloodstream that wicks up the oil located intramuscularly. You inject IM so that your bloodstream can wick up the oil. This happens at a constant rate pretty much, but everyone is different. Quads have more blood supply than other parts of the body. I would never assume that your quads should absorb more than 8-10 cc's a week each leg. However there is the bid question that if your capillaries are wicking up all this oil, what is happening with all of the waste products that your muscle cells are trying to get rid of. Are they able to absorb all of the oil and still absorb all of the waste products or is there going to be a buildup of something.
If you are pinning only quads, in 2 years you may not be able to pin quads. The scar tissue builds up very quick with repeated use. Many guys complain that they only pinned quads and now they can't pin them at all. Delts are extremely easy. VG is easier and glutes are easy. Bis and tris are easy. I don't have enough flexibility to hit my own lats, but I love when someone else pins my lats. If you don't use other areas now you may have to later.