Most fertile days?

So I used OPKs for the first time this month and got a close to positive on the 5th in the am, then retested and got my surge later that evening. I retested on the 6th in the am too to make sure. Afterward glow shifted my fertile week which made Monday, the day I first got my positive surge, my most fertile day. So the day you get your surge is your most fertile day? I thought the day you actually ovulate was your most fertile day? Help please!