Scaled analogue and numerical brittle-viscous shortening models are conducted and the effects of uncertainties of the cohesion of brittle materials in the numerical modeling results are investigated. We demonstrate that the numerical models are very sensitive to small cohesion changes; specifically the geometry and number of structures are variable, especially in models with two weak viscous layers.  The results of some of the scaled numerical models can be very similar to analogue models in the usual range of cohesion values (here 0-100 Pa) of brittle materials.