With regard to (the matter) where the “bitterness” of his ib heart is abundant: This means that his ib heart has sunk, in which it has moved downwards. It is no (longer) in its place.
With regard to (the matter) where the “bitterness” of his ib heart is abundant: This means that his ib heart has sunk, in which it has moved downwards. It is no (longer) in its place.