From what I have read the vehicle weight and the tyre pressure determine the contact patch with very little input from diameter, width or ratio. Maybe jazzaro can bring some of his expertise to the discussion.
There are many parameters to be considered. Basically a tire is a spring, its stiffness depends by air pressure, ratio, carcass and steel belts. The lower is the ratio, the lower the sidewall will bend itself when you brake (weight "transfers" from the back to the front) and you rotate the steering wheel, and this helps the whole tire to keep its geometry. This means that handling will be more constant when weight and temperature change, and the car will be as more responsive as less comfy.
I have an EX, so 185/55 R16, and it's slighty stiffer than the 185/60R15. But it's also more reactive to steer, I can feel it driving fast in hill roads. In normal driving the only difference is confort in potholes.
About fuel economy, I can talk about two cars: with my old Renault, bought with 165/65 R15 and then switched to 185/60 R15, the difference was quite zero, 185 tire mileage was 0,1-0,2 liter per kilometer worst than 165. Mileage used to be worst with winter tires, with 165 and 185, more than 0,5 liters per kilometer, handling on dry and wet road was better with 185/60, while 165/65 were definetly better on snow.
About the current Jazz EX, 185/55 R16 only allowed (in Italy we cannot change tire size without the manufacturer permission), I earned 0,3 kilometers per liter switching from the OEM Bridgestone SP Sport to Continental Ecocontact6, and I lose more than half a kilometer per liter driving with winter tires, same size. So my personal law says that "size doesn't matters", or better, size matters less than the tread softness. But this is my own law, it cannot be a general law.