They will sound better if you can raise them up off the floor, but don't try to get them to "head height." Just look for rigid and spiked stands that will raise them about a foot or so off the ground. Warning--good stands are not cheap. Try Target stands or Sound Organization--both are good.
The reason you want to get them off the floor is to prevent excessive bass reinforcement--try it both ways, and you'll hear that raising them a foot or so will sound a lot better!
Ok so I am getting them off the floor, perhaps raise it a foot or two. The problem is there is no Target or Sound Organization in Costa Rica, but I will look for some good stands in different places. And how expensive are they 50$ or more?
-Victor