New to self-insemination

Allison
Hey everyone! I joined this board because I wasn't able to find anything about self-insemination on the other boards, so I was hoping I could find some support here! My husband and I have only been TTC # 1 for 2 months now, but because he has "delayed ejaculation", meaning he can't ejaculate through sex alone, and has to get himself there "manually", we haven't wasted any time and went straight to using PreSeed and syringes.
My question is about the syringe itself - what is a good size to use? We currently use a 10mL one, but I'm worried it's not long enough so the semen isn't getting deposited close enough to my cervix. 
Is this something I need to even worry about? Do you all use special syringes designed for this purpose?
Thank you!