wheel spacer confusion, 17" 993 wheels Options

[retrotech]

I just got my 17 x 7" 993 wheels. I was told they are a 55 mm back spacing, and I would need 20mm to make them fit
When I measure from the back side its 5 7/8 to rim edge.
I measure my 15" deep six wheel its 4 7/8 to rim edge.
20mm is about 1/2" right? It would appear I need 1" spacer.
Am I missing something? Once again, what size spacer have others used for this aplication?

thanks for your help.

[retrotech]

Thanks for the picture of your car. I think if I had flares I would like better. The 2.25, was a slip on the key board.
Maybe you are right about the fuchs/993 combo, but I could only borrow one tire for fit test.
The 1/2 spacer seems right. Fenders already rolled. Its such a tight fit, I think I might have problems in hard cornering.
I definately want to use Azenis, and in 17" the smallest is 225.
I may regroup with 16" Fuchs and do something different with the finish. Perhaps sand blast for a American Mag look.