Needle insertion question

My urologist believes I need to start using 1/2 inch needles.  He believes that is the primary reason I sometimes do not reach the cavernosa area.  He reached this conclusion after watching me inject myself with a 5/16 inch needle.

I see no anatomical reason that I need to insert the entire 1/2 inch, and am wondering if any of you use the 1/2 inch length but do not insert it 100 per cent of the way.  If so, is there a trick to stopping short that you could share?  If not, I guess I will just use trial and error and see if I can develop a "feel" for it.

Thanks.

p.s. - Moderators, if this is considered too graphic for this particular site, then please delete the message.  Thank you.

Piano, if you are so inclined, I would appreciate it if you would email me.

My address shows when you click on my handle.

Thanks.