That upper BT-20 tube seems longer than the one shown on the face card picture.
I tried to take a picture of the upper assembly at the same angel as the face card photo.
It was reduced until the lower (BT-60) body tube was about the same diameter. This was overlayed onto the face card picture.
It looks like it is twice the length it should be!
The paint scheme profile picture also shows it to be shorter.
Now the questions -
Was the supplied tube longer for stability reasons?
The BT-20 is the same length as the supplied motor mount tube. Was this done just for kitting convenience?
Which length is closer to scale? Does it really matter?
From a quick Internet search, here's the GBU-24 Paveway I, II and III.
This kit is based on the third bomb at the bottom.
The upper tube is shorter than the one supplied in the kit.
A rough guess shows the tube is about twice the length of the upper fin root edge. I'll probably end up cutting the tube.

After looking at side views of the model I ended up cutting only 1/2" off the upper tube.
One wrap of masking tape was used as a cutting guide. An old casing was slipped in to provide something to cut against.
It's a small change but does look closer to the face card and above pics.