My understanding is that the amount of heat energy a parabolic reflective surface generates is not the volume of surface area of the mirror, but essentially the volume of surface exposed perpendicular to the suns rays. This effective surface can be also described as the area of shadow that is cast by the mirror. Example: A very deep conical parabolic mirror has a linear surface area of 1000 but casts a shadow of 500, while a flatter parabolic mirror has a linear surface of 700, but casts a shadow of 600 . The smaller parabolic mirror gathers more photons with the larger "shadow". I've attached an example of two configurations with equal linear amounts, but with unequal exposure. Can someone comment on this? Is my above assumption correct? and a second question .... can photons be compressed?