So I was reading a thread on PF talking about the radius of a solenoid and Bob S answered with a link:

On that site, it states that the Radius = the outer radius - the inner. It doesn't make sense. What happens when there is only one layer of coil and the outer radius (OR) is basically the inner radius (IR). That would create a larger magnetic field than if I had multiple layers of coils and the OR > IR which would then create a smaller one. I don't understand why.

Even in that case, your cables have a finite width.

You can probably consider this equation in the limit r_{1} -> r_{2}, and get a simpler equation for the case where the difference between both is not significant.

In the equation where the denominator is 2(r2-r1). So I'm assuming that the more layers of coils you have, the greater r2-r1 is and therefore less magnetic fields. Which I don't get. I thought the more coils you have, the greater the magnetic field.