And at the first communion, most of the recepients were probably reclining or sitting as was the custom at the time.
I would prefer to always receive kneeling as it is the form of Latria I am accustomed to. But I know when attending an Normative Mass, I must be obedient and receive standing and bow my head as a form of reverence - when I attend the TLM, I can still receive kneeling as that is the norm there and to stand would be equally disobedient at that Mass.
Kneeling, genuflecting, standing, bowing of the head and full bow are all forms of respect.
I have been in many old (very old) missions where there were neither pews or kneelers and standing was the norm historically and currently in those missions.
It is true that once there were altar rails and the norm was to kneel to receive. This was as much body mechanics as anything. One the rails were one means of separating the laity from the altar - a good thing - all communion was served on the tongue - given the variations in size of people and priests, and the height of the altar servers, it was much more efficient to have the people kneeling at a level where the host could be placed on the tongue while the altar boy placed the paten under the chin.
Notice now how awkward it is sometimes for a short priest to serve communion on the tongue to someone who is a foot taller than him while standing. One has to reach up and the other bend down.
Since the indult to receive on the hand in the U.S. has become here, the norm (i.e. more receive in the hand than on the tongue in most parishes), logistics probably had a role in the determination that in the U.S. the norm is to stand. Easier to place the host in the hand of a standing person than that of one who is kneeling.
Anyway one can be reverent in any position - ask anyone confined to a wheelchair.