Thanks for the "width" tag.
I also thought about the AETTR, but in this situation there is too much difference between the frames. If I start to shoot with AETTR always on, then in the 1st direction (from the 6 horizontal + 1 zenit) it will be fine after the sample shots (2/3 shots till get the right settings). The problem is there, that the panorama head turns automatically by 60 degrees after 1 shot, so the AETTR sample shooting sequence will start again and after the 1st sample shot the head turns again... and of course the next frame also different from the previous so everything will be bad.

So it's a shoot-move-shoot head.
The shooting round would be fine till the 2nd direction, it looks like this:
0. (0 degree): AETTR always on, making the sample shots to get the right settings.
1. (0 degree): Start the panorama shooting sequence, result a perfect AETTR shot.
2. (60 degree): Head moved to the next frame, but totally other light conditions, so the AETTR starts again to get the right settings, but at the 1 shot head turns...
3. (120 degree): AETTR believes the it is at the 60 degree direction, but not.

so again...
I don't know what to do, but I think there is solution somehow, that's why I started to experiment with middle shutter value.
Update: The best would be to fix an avarage AETTR setting somehow for all, and fix the Dual ISO too and shoot everything (all the 7) with same settings. Maybe this way:
1. AV mode to find the middle manually by turn around.
2. Find that direction where the expo comp slider shows 0.
3. Switch to M mode: AETTR always on, make the sample shooting sequence and fix the perfect one somehow and setup Dual ISO 100/1600. Can this be done somehow?
Something like this or I don't know. Maybe you understand what I think.