So this set up in flat rate shipping, 16.00+(5.00*([qty]-1)), will increase the shipping amount by £5.00 or what ever currency you are using for every additional item added to the cart.
Is there a way/formula to to add the increase for 3 or more products? So 2 products is £16.00 and then any additional increase by £5.00 per product ordered?

I can’t see a way to change that formula to make it work.