Brake bias gauges

[AlfaSpider]

If I have a car theoretically speaking with twin pot callipers front and rear, 2" pistons at the rear and 3" at the front but also more friction area on the front brakes but same pad material. If I then set the pressures equally say 1000psi front and rear I assume that because of the larger piston size and more frictional area at the front I have a degree of bias to the front brakes? I need 60% to the front and have assumed this means setting the pressures 60/40 but this is incorrect?

[Kozy]

Is this using a twin MC w/bias bar?

How did you determine you need a 60/40 bias?

Frictional area does not matter, area of the pistons does. At present, yes you'll have more bias to the front but exactly how much is a bit more complicated than simply looking at the caliper pistons. Are those sizes in diameter or area? Are they fixed or floating calipers?