yes you are right, I made myself not clear. The 1805 version of the Trotter is not as long as the Revell figures and sadly the other manufactors show. Maybe Airfix made the best try.
The longer version came after the napoleonic wars.
Hamilton Smith made a very good plate with paintings of British knappsacks from different contemporary sources (Genty, Martinet, Smith, Jones). All are showing small, little round knappsacks, not the square ones we have with the existing plastic figures.
Take a look at this link for a description of the napoleonic knappsack.
It shows not the round edges very good, but the size is ok.
We are still speaking about the Trotter knapsack in the Crimean war, but take a look at this link: