As far as I'am aware, colonies have a cap on the number of patrols. Changing the AI feet size cap does not directly affect the actual number of ships in each patrol, the planet's Fleet Size does that. You can increase it by changing the fleet doctrine modifier for the number of ships in settings.json, although factions with ship number doctrine of 1, such as hegemony, will not see any change due to way it is calculated. You may change the indivdual doctrines in data/world/factions folder.
edit: I think this affects other things too, such as mercantile fleets. Just so you know. If you want to make the change just for the patrols alone, I reckon it will require changing the actual classes.