How does the construction project relate to the existing houses that are directly adjacent, or what do the residents say about your plan? Because this can and will be the reason the whole thing fails. And if not before the construction, then after the construction...
What the official says is not worth a penny if he changes his mind tomorrow or has "misunderstood" something. We also built according to §34 and our construction plan had to go through 3!!! instances. Once the municipal council, then the collective municipality, and then the district administration. The first two instances were only recommendations; the actual decision was made in the district administration. So be careful whom you ask here.
Keep in mind that your bunker will become a huge block that will either block the neighbors' light or even cause problems with the chimney distance if you build much higher.
If you want something reliable, then only in writing. I would not rely on anything else. As far as I know, under §34, the architect later bears the responsibility that it was built correctly. So it can happen that an architect refuses to build as you want without a written commitment.