Ever since puberty (which was eons ago), one of my testicles has consistently been "higher" than the other. One will descend depending on heat, but the other remains high (e.g., close to the body). I was never much concerned about this until recently. My fiancée and I hope to have children one day and I'd like to know if my riding-high testicle will reduce my fertility. My fiancée has had a pelvic inflammatory disorder earlier in life, so her fertility is already admittedly diminished.
Given the privacy we associate with our genitals, it's understandable that you may not have compared or discussed your testicles to others. While you may wonder if your situation is unique, it may help you relax a little to know some testicular facts. As males enter puberty, one in 50 boys have one or both of their testes still in the abdominal cavity. One in 500 adult men have an undescended testicle. Similar to what you are describing, most men's testes are asymmetrical, which is normal. In fact, most men's right testicle "rides" slightly higher because human bodies are not perfectly symmetrical.
For normal sperm production to occur, the testes must be maintained at a temperature lower than your body temperature. If your testicle is undescended, sperm production may be reduced and/or maturation of the sperm limited, both of which lower a man's fertility. Other factors which may cause problems of sperm production and maturation are previous infection, such as mumps, chemical and environmental factors, drugs, and a varicocele (a varicose vein in the scrotum). If your testes are simply asymmetrical, sperm production may function fine.
Your concern of your testes shows that you realize the importance of familiarizing your valuable body, specifically the "crown jewels," and any changes over time. Please continue to regularly examine your testes. Consider incorporating a testicular self-exam which takes minutes, is painless, and may potentially save your life (or potential offsprings' lives).
If you are concerned about righty or lefty, it's a good idea to visit a health care provider who may determine the best course of action. Your provider may choose to refer you to a fertility specialist who can assess fertility issues for you and your fiancée.
Kudos to you for knowing your testes and for this advance planning for fatherhood!Alice!