Bugles are a hard way to judge the size of the animal. Most heard bulls once they have there cows wont come into your bugle until you get in his bubble. They will just move off with there cows.
So I say close the distance and mimic him, I have found out once your in his bubble and mimicking him he just cant take it and will come in looking for a fight or wanting to get his cows back. Don't let the size of the bugle fool you and get in there bubble and be careful of him to coming in silent.
Good luck on all your hunting adventures
White Pass Outfitters
really best answer is you just don't know till you see or hear his cows . I've seen a whimpy looking five point run a herd with a 8x9 just laying off . close the distance and replicate the bull .