Seems obvious they'd include the cheapest items if you had multiple things that could be included.
The same way that if you buy 4 items that are all in a "3 for the price of 2" offer, you'd expect to end up getting the cheapest item 'free' and paying for the most expensive individually unless you deliberately pay for them in different transactions.
I'd be very surprised if any of them were ever running a system that didn't preferentially identify the cheapest eligible items to form the deal price.
The same way that if you buy 4 items that are all in a "3 for the price of 2" offer, you'd expect to end up getting the cheapest item 'free' and paying for the most expensive individually unless you deliberately pay for them in different transactions.
I'd be very surprised if any of them were ever running a system that didn't preferentially identify the cheapest eligible items to form the deal price.