Sounds like you had a good night even though a tad disappointing on your side mate.
In your comment above mate, I would say muscle mass and sheer size would be the determining factors, as in my eyes, the physical aspects of the heart and lung capacity are proportionate to the dog whether big or small, if that makes sense A well muscled, strong big dog against a well muscled strong little dog is always going to do well on certain quarry, that's with heart and lung sized being proportionate and even anyway.
Are you going to be looking out for some whoppers now mate?