I'd be saying none of it would be allowable against Case V, and a pretty strong case would have to be presented to convince me otherwise i.e. direct evidence of the level of management involved in generating the rental income.
If you have a look at manual 4.8.3 it contains the 10% concession that Revenue apply to "Investment companies" which have rental income - but this doesn't mean it would apply automatically to a trading company. The presumption there would have to be that the director's duties are primarily in directing the trade of the company.