The unicorns had some disadvantages comparing to the French howitzers. As I have said, the maximum elevation of the Russian unicorns was about 25 degrees. It was difficult to hit a target positioned in deep ravines or in field fortifications. To increase the elevation angle it was necessary to remove the elevation mechanism, but that made the exact aiming difficult. The French howitzers could fire at higher angles and achieve targets at longer ranges.
The amount of powder in the ready ammunition for the unicorns was fixed as well as for the guns. Only the most educated and experienced artillery officers sometimes ordered to cut the covering and to remove a part of the powder charge in order to get a better shot, for example, Ermolov (also spelt Yermolov), the commander of a horse artillery company in 1807, did that in the battle of Eylau, when the unicorns of his company were firing at the manor house of Auklappen to set it afire after it was captured by the French.
In the same time, the cannister fire of the unicorns was almost as effective as that of the guns, and the effective cannister range was almost the same.