"... if it is tied is because if you duck under its head you might startle it causing it to pull back."
Ok, it pulls back and...what? What is the negative outcome?
Have you seen a horse "pull back?" It's a serious thing, I've seen it happen several times so I understand why a person might want to avoid the chance of it happening. You'd think it would be only horses that don't know how to tie, but two of the times I saw it happen it was with horses that had tied solidly for many years.
Horses cope very well with what we ask them, but if they get so afraid that their instincts take over, they will fight terribly to get loose. One horse I saw at a trail ride was battling a trailer and his halter didn't break for the longest time. We couldn't get in there because his hooves were pounding against the metal and he was throwing his head violently back and forth.
The issues are that the halter can release suddenly, and the horse can fall backward and hit his head. The halter can also damage the horse's face or he can hurt his neck. Even quick release knots can get too tight to release when a horse pulls back.
One of my own horses pulled back once, and when my very strong friend could not release the slip knot, the metal buckle on the halter finally broke and my horse fell under the tie rack. Then she stood up right under the rack and knocked herself unconscious. She was OK, but I used a tie blocker ring for awhile to make sure it wasn't going to happen again. Her face was cut a bit from her nylon halter but she thankfully did not injure her neck vertebrae or break any facial bones.
I will never tie a horse solidly in a rope halter, because they are too strong to break. Horses are strong enough to break the metal pieces on a nylon or leather halter.
I also like cross ties but we don't have any right now. I do not use them on slippery surfaces such as concrete because I've had friends tell me about horses that have reared and flipped over in the cross ties, my friend saw one horse die after hitting her head when she went over.
The longer you're around horses, the more you realize ways they can hurt themselves. I've seen a horse cut his head open rearing and hitting a light bulb you'd think was way too high for a horse to reach. I've seen a horse cut all the skin off his lower leg on the handle of his water bucket. I've seen a horse scrape her eyeball on a nearly flat screw head in a stall. I've seen a horse scrape the skin off her back coming out backwards under a butt rope in a trailer. My horse one morning was wearing her plastic grain pan around her leg, somehow she'd stomped her foot through it.