Undoubtedly the unicorns were captured. The Russians withdrew so fast at the opening of the campaign that they probably lost or abandoned guns that they couldn't take with them. They had that problem in 1805 and in 1807. I don't agree with you on the Russian sights. I believe they had to be removed when firing which slowed the guns in action. The Russian gunnery was not as accurate as that of other nations which is one reason that they used more guns than anyone else, substituting mass for accuracy. That is still one of the problems with Russian artillery as their optics are not as well constructed and designed as western systems.
The Russians were definitely loathe to lose guns in combat-all artillerymen were. But the Russians took that to the 'nth degree' and would abandon the troops they were supposed to be supporting if they thought their guns in danger. That was one of the practices that Russian commanders, especially artillery commanders, such as Sievers, Kutaisov, and Yermelov tried to change during the period. Russian artillery employment was defensive in nature and they never caught up with the French in employment, offensive artillery capability, and especially command and control during the period. French artillery commanders would risk losing guns to gain a decisive advantage. You won't fine Russian artillerymen attempting, for example, what Senarmont and Drouot did at Friedland and Lutzen, respectively. Poniatowski was noted for putting his guns in the skirmish line and the French artillery schools taught infantry/artillery coordination, something the Russians did not do. Further, French artillery officers and NCOs were more skilled because of the artillery education system in France, something the Russians were far behind in. Lastly, when the Arakcheev reforms were done, the older gun carriage design that was used by the Prussians and Austrians was copied as well as the older, less efficient screw quoin, and not the elevation screw used by the French and British. But, again, the Russians were considerably behind in command and control, doctrine and tactics, as well as artillery organization, skill, and leadership.