Here is a selection of different size eyepieces to compare the physical size of eyepieces of much the same MM range. first is a 3.7mm Ethos compared to a Explore Scientific 6.7mm then a 11mm ES with a Nagler 12mm and a Edmond Optics 28mm with a ES 30mm.
http://i42.tinypic.com/spdr82.jpg