In the context of your ATPL what they are referring to is eye reference height or design eye height as there are several different names for the same concept.
Manufacturers determine this based on instrument position amongst other things.
Transport category cockpits have a reference symbol that you use to adjust your seat.
In a light general aviation aircraft it’s a little more obvious as to what it needs to be and ‘official guidance’ is not required.
You just need to be able to see over the cowling sufficiently for take off and landing.