Cover line accuracy

Just wondering for anyone experience which app is most accurate for your cover line. First month charting I’m using glow and fertility friend, my cover line on fertility friend is slightly lower than glow. At this point I’ve had dips that have gone below or at my cover line 5dpo, 6dpo and now at 8dpo dip that’s right at my cover line. With fertility friends it’s only been the 6dpo since it’s a lower cover line.

Also should I be worried with this many dips seems too soon to be AF but I don’t know what’s normal for me yet.