Nice deer you got there congrats fellow hunter;) For the most part northern deer tend to be bigger than southern deer,I don't know where you draw the line, a few reasons they are, climate has allot to do with it, very hot climates, the deer don't need heavy winter coats or allot of bodyfat in those area's, so in tern they tend to be very lean, to shed heat from there body cores efficiently, unlike northern deer are the opposite they need thick heavy coats and high bodyfat to survive the harsh winters we have, as we near the winters the deer feed like a frenzy to gain weight for the winter to come, the bigger bodied deer can survive the below zero weather, there thick coats and winter bodyfat keep them alive during the harshest times. There are many more reasons but I believe this is one of the primary reasoning other than good feed. Aim small hit small. RAMbo.