confused 🤯

so i am tcc and ive been using glow since September. my AF is reasonably regular (can be 2 days earlier or late) and i am averaging 6 day AF. now the reason im confused is because some months my ovulation is 3 days after the end of AF and others are a week? this is really baffling to me! i know that charting temp and cm are important if you want to be really on it but in general i would think the ovulation window would be the same approximate amount of time pasted AF?