This means that the further we are from it, the less damage we'll receive.

Their ranged attacks deal distance- dependent splash damage.If you close to melee range, both types of Monkeys attack with claws and teeth instead, but they do less damage that way than with their psionic attack.Though it's not worth spending ammo to take them out, you'll be cursing all the while as you try to bash them in melee combat. While rarely a problem when engaged in close quarters or caught alone due to their low melee damage, when in groups and given enough distance to use their Cryokinesis, they can do a lot more damage. Monkeys are one of the major pests throughout the game, though their diminutive stature actually hides the fact that they can be quite dangerous in certain situations. Monkeys are first found in the Medical section of MedSci Deck and infrequently seen until around the Operations Deck. The neural construction of the creature is similar in nature to psionic human neural structure - the Monkeys are likely to have psionic capability. They are vulnerable to all attacks which affect standard organic creatures. The skull of the creature has been surgically removed, presumably both to prevent cranial pressure and to allow quick experimental access. However, it appears to have been subject to a large number of chemical and surgical procedures, both before and after birth. These procedures have enhanced brain size and connectivity, as well as enhanced the myelination of the central nervous system. The Monkey is genetically normal, an African Squirrel Monkey.

System shock wiki