A. Your implement attack angle needs adjustment - like others mentioned - by shortening the top link so the buster tip angles down towards the ground more.
B. The pic shows the lower links are well up from their lowest. Are you sure that when the 3-point position control lever has been dropped to its lowest, that the lift arms are actually bottoming out while operating the buster? It could be the attack angle makes the buster ride on top of the hard-pan instead of cutting deeper, and those lift arms never get to their lowest.
C. If the 3-point is actually bottoming out while being operated, then move the bottom pins on the lifting rods to their forward position holes in the lower links a few inches in front of the rear "standard" position holes they are in in the pic. The lower links will drop a couple degrees lower and higher than the standard rear holes allow, and lose a bit of lifting power but not noticeable in this application.
The lower link angle will drop the bottom of your buster a few inches. Shorten the top link after changing the pins position to keep the digger frame vertical at bottom position. In my case I use the front link-mount holes for a subsoiler, and our PD15 post digger. With the digger it can actually reach full depth, probably 8-12" lower than the standard link arm pin position allows.