Positive OPK?

Hey girls so last night I got a quite dark positive line on a cheapie opk.. BDed last night just to be sure. Retested this morning line not as dark on the cheapie one but my clearblue digital opk’s has given me a solid smiley face this morning 🙌🏻 I never thought I would see it.. I’m really happy.. it’s my first cycle after a miscarriage in December.. but my question is why do you think the cheap one had a darker line last night as oppose to this mornings test?

Pic below, any advice would be appreciated x