Questions about fertile window

I have a question about my ovulation day since I’ve been noticing that I have egg cm from day 13 to 15 while ovulation tests are positive from day 15 to even day 17. My cycles are usually 28/29. I clearly tend to ovulate late right?

I don’t understand why I usually have the egg cm so early then (I thought it appear right before ovulation and in my cycles there’s sometimes 1/2 days in between)

It’s confusing because every cycle that my egg cm appears I think I’ll ovulate soon but then the ovulation test has been positive usually 15 and 16 (one time on the 17) meaning I’ll ovulate in 24/36 hours.

I’ve been bd all these past days and today I decided to do the ovulation test just to check and it was positive!

So I guess today is the day.

Does someone also has this cm so early?

Thank you I’m still new discovering when do I ovulate.