By reducing the speed of blood flow profiles the dependence of Ht on the radius of the vessel becomes more elongated. However, at normal values of Ht, the effect is also insignificant. With high enough shear rates, the red blood cells become susceptible to deformation.
Adjusting the speed of blood flow changes how Ht relates to vessel size, making this connection more direct. Nonetheless, at standard values of Ht, this effect is inconsequential. At high enough shear rates, red blood cells can be stretched and deformed.