For those of you that don’t get progressively darker test how are you sure when your fertile window starts?

I’ve been using opks for 2 months but really started tracking right after my period last month. My lines stay about the same until the day before my positive then I finally notice them a little darker.

I use clearblue advanced and easy@home last cycle. Clearblue gave me high fertility for 9 days so I feel like we wore ourselves out w the bding before my actual fertile window. The app seems to be about a day or two off from when I actually ovulate so I don’t know to try to go by that and hope for the best or what. I just want to make sure we do it more before peak & ovulation day.