Please study the plans of the AnXI howitzer. It could not be elevated as much as the old Gribeauval Carriage. Details of this are in Gassendi (1809) and no doubt repeated in 1819. Having drawn then to scale for NGA Archive. There was very little difference in the elevation of the Unicorn and the AnXI 24-pdr Howitzer.
Now to which unicorn and the date do you refer? This makes a difference.
You have made th statement that the French had Unicorns in their artillery park but where does this interesting fact come from. I have not seen returns that indicate this.
Borodino was in effect a draw. Both sides had almost exhausted themselves. Kutusov had done what he could and drawn the teeth of the Grande Armee that then as it could no longer feed itself died slowly. Moscow was an empty victory.
Why fight a slaughter when he still had an army in being to fight again upon better ground. Borodino was a plain. There were some fortifications. I have asked questions as part of a discussion. You have restated what I have challenged. Yes I have read those books that you have indicated. I think you need to look into the background of Wilson a little more. He considered everything that was British as superior. He spoke no Russian. The writings of Clausewitz are enlightening.
THe Russians used their guns in a different manner in 1807 to 1812 yet there is always this statement upon 1807.