In theory, you should aim a bit low, but at our ranges, it makes no difference. i.e. if you aim 1/4" low, but your crossbow shoots 4" groups at that distance, who knows?

On the other hand. . .Crossbows are noisy, so you should expect some deer flinch. They tend to flinch down in the initial move to take off. That can be a 2 - 4" drop. I have always been told to aim 2 - 4" low to avoid a high lung shot or back shot.