You chose a bad example, as the in “small” battle, the defender doesnt have an artillery. Get two battles, same unit mix, different size (1inf 1art vs 1inf 1art … 2inf 2art vs 2inf 2art) and see, how both battles are affected same.
Yes but mathematically, a battle with less units will vary in victory percentages then a battle with more units. 1 inf and 1 art vs 1 inf and 1 art will likely be so different as a normal amphibious assault, whereas a 10 inf and 10 art vs 10 inf and 10 art will be dramatically different, because you are channging the dice values for 20 units, where as in the small bale, you are only changing the dice value for 2 units.