If the motor has a label of 1.8A, that is a max, and does not mean that you need to actually have 1.8A in it to work. However if you insist to get close to this number, both stepper driver chips and the motors will run quite hot, and under worse operating conditions you have more chances of bad stuff happening.
The point of adjusting the motor current, is to find a minimal current level at which your mechanics function normally without missing steps or without any issues. The aim is to get this minimal level for many concerns but also for efficiency. Any current more than that is basically wasted.
I would set the vref to a low level, like for a current of 0.5A, make some observations, then increase perhaps to a level like 0.8A, afaik i think the latter number is reasonable for most machines. Perhaps for z and extruder to have like 1.0A and x and y 0.8A, or anyway something like that range. At least my opinion.
The point of adjusting the motor current, is to find a minimal current level at which your mechanics function normally without missing steps or without any issues. The aim is to get this minimal level for many concerns but also for efficiency. Any current more than that is basically wasted.
I would set the vref to a low level, like for a current of 0.5A, make some observations, then increase perhaps to a level like 0.8A, afaik i think the latter number is reasonable for most machines. Perhaps for z and extruder to have like 1.0A and x and y 0.8A, or anyway something like that range. At least my opinion.