Head position varies with discipline, and with what is natural for the individual horse. The Thoroughbreds I have known tended to carry their heads lower than the Arabians I now have, and the Quarter Horses lower yet. If your horse is properly collected and paying attention, I would not fret over it, unless you are showing and even then it can vary depending on what the judge happens to prefer. Not very helpful. As to bucking, my Arabian gelding can buck very well with his head up. Ear position is very important, and you should also be able to feel what your horse is thinking with your legs, seat and hands. If he wants to buck, you should be able to tell before he can act. If not, where his head is wouldn’t be a factor. In the Dark Ages, when I showed hunters, the preferred position was neck extended more or less level with the withers, and a relaxed but collected horse. I don’t know what is in style nowadays. And, even with the same discipline (pleasure horse, for example) some breed shows are looking for a higher head carriage than others. So, if you are riding just because you enjoy it, and you and the horse are both comfortable and you get the response for which you ask, it is not a thing I would obsess about.
It is never the horse's fault