Can back surrounds smear the front image?

I'm yet to be convinced of that the addition of rear surrounds represent a general improvement. Theoretically, I realize, it should. And certainly it does, for specifically encoded rear effects (few and far between though).

But in my set-up, I get a smearing of the front image (reduced clarity and definition), a constant problem. My rears are directional (Revels), not dipoles or bipoles.