note the v shape at the end of the clipper line.
You clipper the top third of the overall length. NOT the leather, the overall length.
Proper ear set should be at the eye or slightly below the level of the ye when the ears are laid down.
If the dog has high ears you may clipper lower, lower ears you clipper a bit higher.
The shape of the ear is actually a "V" shape, not a straight line and it is done with a ten backwards on the OUTSIDE of the ear, and I use a 30 WITH the grain on the inside of the ear following the same line as the outside and trim the edges with shears to give it a tidy appearance.
By holding the ear FLAT in my hand as I clipper I am able to get a good line every time. It is important to note that clipper lines should extend slightly up onto the crown of the head as you approach the top of the ear.
Ends of the ears should be rounded slightly after the groom is competed to give them a more finished look.
The drawing on the ears in this shot should give you a good idea of the placement and shape of the v on the ears. her ear placement is actually VERY nice.