From my experience it's better to setup the IP company as a completely separate entity. There can then be a contractual relationship between the OP company and the IP company.

This will assist in protecting the IP in the case of any legal action against the OP company. For instance, if the OP company is sued due to "bad advice" then the IP is not part of the law suit. The challenge then is to ensure that the directors of the both companies are different.....as any law suits of this nature often end up throwing the directors in as well!

This structure gives you the greatest amount of flexibility in your business in the event of a sale. Quite often a purchaser wants the IP but not any of the potential liabilities (or skeletons) of the OP company. You can sell the IP company off as a clean entity and gracefully close down the OP company.

I wish you all the best in the venture!