Alright after some research and loading one by one all the mods i find out that the Archean Order mod cause the limit to revert to 500, i search in the mod files and find a custom setting.json that override the classic one on certain part, here the battlesize. This explain why my modification to fps and fleetsize take effect but not the BattleSize.
So if someone have the same problem go to your mod folder, Archean Order and follow the same route as you search the setting.json in vanilla. You should find the custom one and make your modification.
Have a great day !