Yes, it does. The vigin conception Is what makes it a virgin birth. The virgin conception is given in scripture. without any such similar evidence, the birth as a "light through a window" is pure invention.
"At which point did His existence in Mary cease to be a miracle and just an "ordinary" event to warrant an ordinary" Birth?"
That would be when a viable diploid egg was present.
And the idea that a limitless and eternal God would appear in time and limited in space, enter her womb like light through the glass is of course perfectly factual and credible.
If her pregnancy was without physical entry, why would a Birth lacking physical exit not be possible? That would be when a viable diploid egg was present
A 'viable diploid egg' is an oxymoron, spunkets. An egg is a haploid, by definition, and the fact that women lose at least one every month (if not fertilized) during their menstrual age means it's not viable.