Sorry the DB helpdesk is based on pure unpaid voluntarism, any comments here posted are donations of kind, caring, emphasizing people, who are happy to share and learn themselves.
I'll give it a shot.
First I think the difference is not huge, actually it's normal for beginners.
1) How long have been practicing freediving?
From the information you give, I think it's basically a question of more CO2 training and time to get comfortable.
From your words I got the impression that during your static you may be a bit too much focused on time and or the anticipated contractions etc. Maybe you're now getting your mind programmed, your body conditioned to react to a time instead of an impulse.
To counter this you can leave the watch to your buddy, and have him not tell you about times until you've done you last dive. Instead of making a timed schedule you can go by 'effort level'. Your Table B might look like: 50% - 60% - 70% - 80% - 90% with 2' intervals. Doing your dive without packing also greatly increases comfort.
You position in the water is also to be considered.
Food preparation, time of day, previously done exercise, hydration and more things I cannot think of right now.
Feel free to bring more data to the table, because the info here above feels like only a part of the equation.
BTW You can view also the difference as a positive, knowing you have enjoyment of more future pb's on your way to that big 7'!
Patience is what we need my friend
Love, Courage and Water,
Kars