I understand what your saying, my point was if you start heading towards a more bully type (looks, head size chest etc) your steering away from a typical working terrier and your taking on more than the bully looks. A good working terrier in my opinion will have as much drive, determination stamina and above all hunting instinct than any bull so why go down that route. I’ve worked and bred plenty of terriers with a % of bull in them over the years and by no means has it improved any workers.