Hi Jakub,
What I'm suggesting is as per the attached modified photo of your door panel. The black bit at the bottom could be left in the door frame and marked "Remove after Assembly".
The problem I'm addressing is that I feel it is essential to get the brick Bond to mesh correctly and fully to ensure the join is as invisible as possible and with my level of dexterity it is proving to be more challenging to do the door section which is less stable than the similar sized windows, for example. It is also possible to over stress the junction between the side and the top of the panel and this would also be helped by the stiffener.
I don't think your instructions are all that bad. Perhaps more emphasis on The Manual & Guide would be useful as I suspect that most people will be modifying your designs to suit their individual needs.
Regards
Ian