Man, hard to say without being there. My old 797 doesen't really show
brush all that well. You've got to come by it not too close, not to far away,
and really be looking. Brush shows just fuzzy, ghostly images on mine,
hard for me to tell from baitfish. Big trees now, stick out like sore thumb.

On the downward, only ideas I'd have is check the fish id sensitivity setting,
and play with the front/back angle of the transducer.