The "unit" of the depth is 1/4 of a click (64 "game units"), so for each click there are 4 "depth units". And for one sector there would be 4*4 = 16 depth units. However, as stated in the formula, the depth value must be multiplied by 256. So if you want a 4 click depth, you have 256*16 depth units, which gives 4096.