Chris is saying 200 ships shouldn't find cause to attack at all, yes. What would free them in the first place, aside from CPAs? Their default behavior will be to guard their own planet from attack, not to come after you. Unless you do something to upset them, like shooting at their command station...
'Low surface area' means simply minimising your hostile front - you want as few of your worlds bordering the AI as possible, really. Sometimes it's unavoidable and you have to necessarily defend multiple ingress points but usually you should be able to take planets in such a way as to create only a few chokepoints through which the AI might send ships.