Nolaria plays out combat on a one inch grid map. Movement and range are tied to this scale, as defined by the 5e rules.
The DMG p.249 illustrates creature size relative to squares on a combat map. For the purposes of playing out combat using miniatures:
Except in the case of tiny creatures, squares are defined to be fully occupied. While this is not realistic, it does conform to the 5e combat system.
Shooting "through" a creature to hit another one provides cover. Cover is defined on p.196 of the PH. Note that the example of half-cover is, "The obstacle might be a low wall, a large piece of furniture, a narrow tree trunk, or a creature, whether that creature is an enemy or friend."
A ranged attack through a square occupied by a tiny creature does not give cover, but through two tiny creatures counts as one square, thus giving half cover.
Ranged attacks through a single occupied square gives half-cover (AC +2 and DX save).
Ranged attacks through two occupied squares gives three-quarters-cover (AC +5 and DX save).
Ranged attacks through three or more occupied squares gives full cover (attack not possible).