I would say it is not about "above", but the mulch should be kept 2-3 inches away from the graft union or trunk of the rose, whether above or below the graft union, - horizontally.

Jackie

Agreed. Mulch can keep the canes/union too wet and help lead to canker and other issues. You honestly don't need mulch much past the trip zone of the plant. Usually, a well leafed out rose bush will shade the soil sufficiently to prevent it from overheating, losing water and giving weeds a chance to grow. So, definitely mulch, but keep it probably half way under the drip zone (where rain water would fall off the leaves around the outside of the plant) out to between the roses so you have that insulation, moisture retention and weed barrier without keeping the ground level parts of the plant too wet. Kim