In our experience, a fine grind, or espresso grind works best. Why? The espresso grind will create a greater surface area for the water to infuse and will result in a richer brew from your Aeropress than a grind that is coarser.
The inverted method for Aeropress is from the Ronseal school of descriptions — it does exactly what it says on the tin. In essence, instead of adding water to coffee, you add coffee to water simply by flipping the machine upside down. To explain, you grind your coffee (espresso-style is best) and place it in your Aeropress. Then add your hot water and press.
There are subtle differences between the normal Aeropress and inverted but there is definitely a difference. With the standard method, water drips through the filter immediately after it has been poured over the ground coffee. With the inverted method, the coffee stays in the water for longer which means more flavour will be extracted for a richer brew.
A coffee purist would say that espresso cannot be an Aeropress by definition. And, by definition, espresso is ground coffee which has a layer of creamy foam (crema) which is a result of the brewing process. The Aeropress method will not produce this creamy layer. However, does the Aeropress method produce a strong coffee similar to an espresso? Absolutely. Just don’t ask where the creamy part is.