Your uxter plate will indicate depth at stern (more or less) and it will be a few inches less at the bow (obviously this measurement taken at a point where the baseplate is still flat) .
If its a sink then the skin fitting will have to go where it needs to be- the sink itself will take into account your required 10 inches.
If its a skin fitting to say a pump, then leave some spare hose to loop above the fitting- you can always adjust to suit later.
If in doubt, as Wotever says, wait until its in the water!