I think mseds99 was using the shield to hide from the breath weapon. When granting full cover, it fully protects against area effects. At 9/10 cover, it effectively grants Improved Evasion, in addition to the +4 Reflex save bonus.
Exactly, I should have clarified. When I used it to protect verse dragon breath, I would hide COMPETELY behind it getting total cover, while casting buffs with my free hand. When shooting with the crossboww, we say that t grants 3/4 cover. For simplicity's sake, we don't play that a cone angles in to the character after it bgets blocked by the tower shield. That seems like a bit of realism-overkill, but as they say...to each their own.