Transmission Tuning

How do engineers tune a transmission for the cars engine, acceleration and top speed, and other factors?

Are the gears adjusted to be operated in the upper percential torque band of the engine or some gears for acceleration some for fuel economy, and top speed?

Or heck how are modern drive trains geared for operational performance efficiency durability and space?

I know having a 1:1 ratio on the differential would be hard to gear in a transmission because you would need large gears.

they try to balance performance, comfort, and economy in their selection of gears. How performance oriented the car is determines which one they emphasize.