Fortunately, I don't have to criticize Jungmann--you already made clear the basis of the following text.
More seriously, I seem to recall a recent article discussing Church architecture, laying out the differing styles over time (perhaps Latin Mass magazine?). The article indicated that the Communion rail was a later installation, as Jungmann indicates.
HOWEVER, the question that neither Jungmann nor you have answered is whether this kneeling was "forced upon" the laity or whether this is something that was spontaneous.
It is also possible (from the text you cite) that the Communion rails were installed as a response to the laity's already-existing practice of kneeling for Communion. (My own theory is that they were installed more as a line of demarcation for the 'holy of holies,' similar to the gates found in the Eastern rites, and to the layout of the Temple.
Pending further info (for which I have sent off and should have response in a couple of days) it will remain an open question, I suppose.
Summarily: your citation leaves open TWO possibilities: one, that the laity were "ordered" to kneel; the other, that the laity were kneeling in the first place, and that rails were installed as an accomodation.
Be that as it may, forcibly changing an otherwise harmless practice is absurd and reeks of authoritarianism--the "I'm the boss, do it my way, regardless..." sort of crap that engenders resentment. If the laity were "forced" to kneel, that was wrong, EVEN THOUGH I, personally, prefer the kneeling posture for its implicit self-subordination. Standing, regardless of the propaganda being circulated, is simply less so, viz., the practice of nobility to kneel in the presence of the Kings as a mark of fealty.
One might also remark that in the American culture one stands for judges and Presidents--as opposed to the European culture's kneeling, still practiced to this day before the Monarch of England.
Why do I bring this up? Because "Americanism" is the specific topic of a monitum from Pope Leo XIII (??) and may actually be the underlying thesis in this controversy.
He is unable to find or recall any documents which indicate that there was a 'forcible' aspect to the kneeling apparently arising in the 8th/9th centuries.
Part of the larger problem is that there is simply little (or no) documentation to support the "factual" statements of liturgical reformers. They simply propound that "XYZ is fact" and we are supposed to accept it as so. When research demonstrates that either it is NOT fact, or that it is merely speculation, the credibility of the reformers is eroded.
You may recall that 15 years ago, "reformers" postulated (as fact) that not only were priests married until some draconian disciplinarian stopped the practice--but that there were "deaconesses," which were ladies who were ordained.
Five years later a scholar refuted every single "fact" that the reformers had postulated--and he did it with documentary and irrefutable evidence. While it was a fact that some priests were married, they gave up relations with their wives. There were 'deaconesses,' but the title did NOT indicate ordination--rather, a vocation (in this case, health-care.)
But in this discussion, you have made the statement, thus you still have the obligation to prove: that the laity were "forced" to kneel against their tradition.
Ball's in your court.