Who can help with offset calculations?

[JS_4.8]

I just installed a set of 4 20x9.5 replicas 87's with Pirelli Scorpion Ice&Snow 275/40/20 for my new winter setup. Dry handling has been great, although havent had any snow yet in NJ to test out the snow capabilities. Obviously the looks department is a huge step up from my previous 18 inch winter setup.

With a 9.5 wheel in back with a 45 offset, same as stock fronts, does anyone know how much of a difference this makes in moving the wheel inward? Meaning narrower wheel, but bigger offset I believe than stock 20x10.5 rear wheel.......so how many mm's has the whole wheel/tire combo moved inward? Trying to figure out if I should get some spacers back there or if its basically the same stance as before.

Thanks!