What a pity we don't have photos or drawing to show what she meant. Seems that, like me, you disbelieve what she said. Difference is I believe Linnie and Buell were lying about the bag. You seem to believe that they both saw the bag but don't believe their estimates of the size.
Actually it's easy to understand what Randle meant, at least with how the bag was gripped. A few months ago I thought the bag might have been carried with a choke grip, and slightly bent arm. I tested that myself at the time... but, that doesn't make sense if he was trying to reduce the package profile. Seems Randle's carry-description would keep the bag right beside him.
Based on Randle's first-day report of an approximate 36" bag length, her brother's rather aggressive handling in interrogation, and then the incredible shrinking bag popping up, one can reasonably argue that FBI/Dallas weren't the only folks taking a CYA stance. So I'm not unreservedly calling them liars in the nasty sense that Johnny666 and others here use. I'm more inclined to place them in the 'white lie' category, as there was never going to be a trial anyway, and Buell had to live down the fact that he drove the potential killer to work that day.
Alternately, as JohnM has just posted, the approximations are in the ballpark as compared to the Rather demo.