Knowing the skirt length coverage of 12cm and 4cm down is where your target is, all you have to do is position yourself at an appropriate distance and height, and you will see what you want to see.
obviously, the key is to have the lowest sitting height. at the end of the explanation, it mentions that "without lowering the eyes by 17cm, you cannot see the 'inside' but in order to see, one must lewdly put forth the pelvics by 45cm. (by doing so, you are leaning back so your head is lowered)
If the observer's eye, E, lies on the extension of BC, you can put the point B in a clock. If you form a right triangle DEC by forming a perpendicular line to the line BC, it will create the following figure, formed by two right triangles. In the Triangle ABC, AB is 1/3 of AC; therefore, DE becomes 1/3 of DC as in Triangle DEC. DC is a horizontal distance from the observer's eye to the end of the skirt. If we assume this to be 1.6m, DE, the height of the eye, will be 53.3 cm away from the skirt. If an observer with height of 170cm was to look, sitting height being 70 cm, will not be able to see the inside unless he lowers his head 17cm. To see, he would have to explicitly push his butt 45cm forward.Assume that connection point between the thigh and the skirt's inside is 4 cm, and the connection point between the end of skirt and the inside of the skirt is 12 cm. If you look from the side way, the targeted area and the skirt forms a right triangle ABC.Miniskirt in TrainImaginary (or fancyful) Science Colletion! 2nd edition