In my experience, 'Optional' refers not to an option of a different pressure setting but more to optional size tyres that may be fitted to the vehicle.

So if you have 15" tyres and the pressure is 36/41 I would guess that the 'Optional' settings may refer to an alternate size (such as 16")...

Best method is to go for a long drive and check tyre temps across the tyres. They should be even across the width of the tyre when the pressures re right. Too high in the middle says the pressure is too high, to cold in the middle says too low. Its normal for there to be some variation side to side but if you really want to be clever you can use the temp side to side to set wheel camber angles....

If you haven't got a temperature probe try looking at the tyres wear. Worn in hte middle is too much pressure, worn on the edges is too low pressure.

A.