Small compared to what?
Aside that that theory left out the accounts which said the ship break at the surface it ignores several derbies pieces. I only watched it one time (as it was really bad) but if I remember right, they ignored the debris going to the south (and does not explain the large parts to the east). However the theory was not a new one, it has already published in the late 1980s I think and had been shown to be wrong. Sure there is a discussion here on ET somewhere.
I think what is forgotten in that documentary is, the debris we are talking about isn't just wood and paper. Its tens of thousands of tons. This has to be taken into account when looking at the size of the debris field.