There is no mention of size-related modifiers in the SRD or CRB, but PCGen is applying them to AC and both Melee and Ranged Attack Bonuses.
For example, a Level 1 Hover Drone (Size = Tiny) should have an EAC of 14 (11 base + 3 for a 16 Dex) and +4 Ranged Attack Bonus (+1 BAB, +3 for a 16 Dex). However, PCGen is giving an extra +2 Size bonus when looking at both on the troubleshooting.htm.ftl character sheet.
It also seems to be applying the Size bonus for Stealth.
Because the information does not exist in the SRD/CRB, I can't point to an official source for it. Relevant discussions are at https://www.reddit.com/r/starfinder_rpg/comments/70wgq4/stealth_size/ or http://paizo.com/threads/rzs2um94?Size-in-Starfinder-rules