since the values are meaningless to me, and it 'displays' a value, the syntax is fine. Since you mentioned that the value is in the wrong column due to its sign, why not use the value to determine which column it goes in? It would appear that {ichist.homeextcst} would be the variable that would determine which column to display value in. You can still use the ABS () function, which always displays positive, if you like, though it won't be needed in one of the formulas as the values will be by definition positive.
You would need 2 formulas, one for the increase and one for the decrease, they would look pretty much the same, just checking on that field.
HTH