I don't have BfB to check in-game, but according to the game files the result you get is determined by the decision you run, not the other country's response (they can choose to say no, but not what the investment is if they say yes). The various investor nations each have multiple available decisions, and for most of them the first decision only gives a slot but the others give factories. The better ones are also locked behind later focuses - you can get a slot from Britain with Open Up The Country, but you need British Docking Rights for factories.
For Britain, for example, Inviting Entrepreneurs will get you a building slot, Trade Showcase gets a factory, and Ship Parts for Investment gets three off-map factories.