A lot depends upon yourself (age, any back problems etc.) and what you find as a comfortable stance, my machine is some 80mm or so above the 'norm' of elbow height.
Reason, I can stand more upright for most tasks and avoids back discomfort that I get when it's lower and have to keep bending over to look inside pieces etc. (swivel head machine is a boon in this respect)
It does alter the tool presentation angles but again it's what is most comfortable for you and feels natural, does not stop you using body support and swing, may alter the tool nose angles and wings but once again it's what works for you and they will probably be different to mine or your mates anyway.
So my take on it is to start off at the 'norm' of elbow height but with the option to raise the bench/stand whatever on blocks if needed to relieve stance discomfort.