It seems there was a mistake in my calculation so that I can have a 45mm regel anyway... The U-blocks that make up the last row are only 19cm as opposed to the Exakt-blocks which are 197mm. I had calculated based on a 20cm height.
With 45x220 it becomes too short to have anything to screw into, so I will still go for 2 x 45x145mm in width as sill where the innermost one is screwed into the U-blocks with expansion bolts about cc60. And then attach the floor joists with angle brackets to the sill cc60 as well. The outer 45x145 is mostly filler as I previously drawn.
If anyone thinks it’s crazy, feel free to say so.