How tall is Rather compared to Oswald?
Rather wrapped the bag tightly around the barrel, to reduce the size of the visible part. There is no evidence that Oswald did the same. In fact, iirc Randle said Oswald was holding the top of the package which was folded.
Frazier could only have known that Oswald carried the package under his armpit I he actually saw Oswald put it there. If he had seen Oswald's back he couldn't know this detail.
Q: Tell me, how was Lee Harvey Oswald carrying this package you described
as he was walking in front of you?
A: Parallel to his side, up and down. Like you stick it up under your armpit and
the other part cupped in his hand.
Q: Did you determine whether it was in his armpit or were you close enough to
see that?
A: No, sir, I was not close enough to see. I didn't pay attention to it particularly,
but as he was walking along in front of me naturally I looked in his direction
and that is what it appeared to be from what I saw.