Huh! Thank you for seaching for me. 
Why did I not not think about a solution like this?
I am sure, this will solve my problem. Thanks again.
Btw. I as well use an additional LED strip (powered by the internal USB) that sits above the roof glass underneath the rised AMS. Yes, it is not as bright, as I wish. On the other hand: Old eyes (and so are mine) tend to need much more light than younger ones. This means, my rooms are enlighted very bright as well. May be this makes the difference.
Nevertheless, thanks for your help.
Happy printing.
Frytz