capacitance - Why can rolled up capacitors be modelled as flat parallel plates?

If you have two parallel plate of opposite charge with a dielectric in between, then

Capacitance, $C = \frac{A \epsilon_{0}}{d} K$, where $K$ is the dielectric constant.

This is used to calculate the capacitance of a capacitor. However, a real capacitor is actually two of those plates rolled up many times. Wouldn't the electric field $\vec{E}$ be different?

So why is the equation for the capacitance still valid?