Car appreciation... the aesthetics, the engineering, etc

I need some reassurance im not effin this up.

So im getting a spacer going by feel as the wheels cant be test fitted to measure what would works better with the wheels in place.

Old rear wheels = 8" with ET of 33mm
New rear wheels = 9" with Et of 53.5mm

Im sure theres a much easier way of thinking about this but here are the thoughts keeping my up :)

The old wheel was 8" = 20.32cm in width total.
The centerpoint of this rim is at 10.16cm.
But since the Et is 33mm the wheel would "protroud" inwards from the mounting point of the hub with a distance of 10.16cm+33mm = 13.46cm
So the rim edge would end up 13.46cm in from the mounting point.

The new wheels is 9" = 22.86cm
The centerpoint of this rim is at 11.43cm
But since the et is 53.5 mm the wheel would "protroud" inwards from the mounting point of the hub with a distance of 11.43cm + 53.5mm = 16.78cm.
So the rim edge would end up 16.78cm in from the mounting point.

The differrence between the wheels inwards protrouding length (theres likely a better word here that i cant come up with) = 16.78cm - 13.46 = 3.32 cm

Thats quite a lot. I guess this means (unless im thinking wrong) that the outer edge must be (since the new rim is 1" wider) 3.32 - 2,54 = 0.78cm more inwards than the older rim despite beeing an inch wider.

Now a 18mm spacer (the thinnest they can make for a spacer that changes bcd with the new center bore diameter) would make the new rims outer edge sit at 1.8cm - 0.78cm = 1.02cm more outward. And the inner edge of the rim would now be 3.32cm + the spacer of 1.8cm = 1,52cm more inwards than the older wheel. Which seem correct since 1.02 + 1.52 = 2.54 = 1"

Now providing this is correct does that seem like a good way to start with a spacer, just say yes!
Ha dont want to go more outwards and they cant make a thinner spacer so i guess thats where im at if my math is not bonkers.