.5 IS a little small. But with the choice between .5 and 4 . . . one of my biggest objections to holding this at the Shirlington dog park was that the size of the place made keeping and eye on and controlling your dog very difficult. Frankly, I couldn't turn to answer a question from someone or pet someone elses dog without Sarama going behind a tree, around a bend, or dashing off with another dog. Which was fine, that's why we were there, except I really, really wanted to keep an eye on her while she did it.
Since half the point of this is to meet each other, I'd prefer a more easily controlled enviroment, where we can look out of the corners of our eyes, rather than have to follow our dogs around. Although you can keep an eye on four flat open acres, I don't think that's the description of this place.