Why is using a thin makeshift tourniquet (leash), or small width tourniquet bad? It's because of the pressure gradient.
In the case of tourniquet use, the article explain and shows that the width of tourniquet is a very important factor. Wider tourniquets are associated with less complications, better pressure gradients, and less pressure is needed to stop bleeding. The smaller the width of the tourniquet, the higher the pressure gradient needed.
OMNA's tourniquets have widths from 1.5" to 2.5" inches or 3.81 cm - 6.35 cm to provide better pressure gradients.