Just like any other horned critter if you are looking for high B&C score there are 8 mass measurements. Mass is definitely important but it takes just about everything to make B&C. The top 2 mass measurements are just as important as the bottom 2 and I don't know how many bucks I've shot that just missed book because they didn't have an inch here or there!
Different states and regions within states "generally" tend to produce different genetics and horn confirmations. If you go to a local taxidermist where you'll be hunting take a tape measure along to get a feel for what antelope from that area produce. It also helps to scout well in advance of the season so you have an idea what an average buck looks like. After viewing 50 to 100 bucks when you see a monster he'll really stand out! It is somewhat easier to get a close-up look at bucks prior to the season when they start getting spooked. I often look at bucks at point-blank range through my spotting scope when I archery hunt them from waterholes....this really gives you a good idea of measurements.
I hunt Wyo quite a bit and the minimums I look for are 7" bases and 2nd qtrs, 4+" 3rds, and 2 3/4" 4th qtrs. Prong minimums of 6" and length of 15 1/2". If you add all those up it is pretty close to B&C minimums. I try to find bucks that are super massive, 15+" horns, and 6+" prongs. If they meet that criterea they are worth a closer look.
I wouldn't even attempt judging antelope without a high quality spotting scope. Horns come in different shapes. Some have oval shaped bases while some are nearly round. It is also important to get several views of a particular buck from different angles, front and back. Like most game the worse view is from the rear!
I have never liked the idea of using ears, nose, or eyes to estimate mass or horn length on any game species. This has screwed me up more times than not. Just like on humans ears, eyes, and even heads/bodies come in different lengths and sizes. If you look at a buck from different angles or if he tilts his ears a certain way you will come up with different measurements.
Prongs that are high on the horn rather than low often make a bucks horns look a lot longer than they actually are. Often bucks with prongs that branch off high on the horn have very short tops. Some prongs are a lot more webbed than others and if you find a incredibly massive buck the mass or bladed bases often adds on to the prong length.
I have always liked to compare measurements to a dollar bill. A $1.00 is 6" in length. Prongs of 6"+ are pretty much required for good score. Also if you can wrap a dollar bill around the base you aren't looking at a whole lot of mass.
Just about the time I think I have everything figured out I shoot a buck that totally fools me...dreaded ground shrinkage! I've been hunting them for about 35 years and it still happens!