"I tighten my chain so that I have just a tiny bit of play at the tightest point, which gives me about 5/8" play at the loosest point."

If you have this much slack how will the chain not come off more easily?

"As for a chain coming off easier with a biopace ring than a chain on a round ring, I don't see it.
My chain won't come off unless I loosen the chain tug and the axle nuts."

I had to set one of these up for a customer, with the chain tight enough to pop I could easily derail it in the stand.

I glad Biopace works well for you. I just dont think it should be recommended for fixed riding.