Hi FranklinsAce, welcome to the Forum.
I just happen to have some of the same size magnets and did some testing using metal plates of different thickness.
For the 1" x 1/2" x 1/8â€, a plate of 1/8†is adequate.
For the 1" x 1/2" x 1/4", a plate of 3/16†is adequate.
If they were weaker than N52, you could get away with a bit thinner plate.
As far as I know, there is no formula to find the thickness of the steel. That is why builders go with the paper clip guidance.
It would be possible that someone could write an equation for that purpose. However, they would have to do it after extensive testing to get the data, because there are too many variables. Magnet area, thickness, magnet grade, just to name a few.
We would love to hear what you are working on. We are all here to help each other and to learn from one another.
Ed