Is there an advantage to the oval swivels over the standard round ones? I always change the oval ones out because when I tie onto an oval I feel that the knot is too close to the "starting point" of the swivel, no matter what end of the oval you use. I am afraid that the knot might slide onto that point causing the knot to fray and weeken. Am I altering the action of the lure by changing the oval swivel out? Can someone please advise? Thanks.

Oval split rings were designed to prevent the very situation you fear. So you're undermining their purpose. if you are that worried about it, cut the split rings off, and use a Duo-Loc snap.

Your thought process is backwards.