We define a knot to be \(\gamma _0\) -sharp if its Seifert genus is detected by the concordance invariant \(\gamma _0\) , which arises from the immersed curve formalism in bordered Heegaard Floer homology. We show that a connected sum of \(\gamma _0\) -sharp fibered knots is ribbon exactly when it is of the form \(K \mathbin {\#} -K\) . Consequently, either iterated cables of tight fibered knots are linearly independent in the smooth concordance group, or the slice–ribbon conjecture fails.