True, but the interstitial pressure of a compound or emulsion is also dependent of the presence of micelles, as I presume tar is made up of various length hydrocarbons, some of which will be relatively short chain oils, among a soup of other organic compounds

Plus there are several types of “Tar” Pitch/Coal Tar are even lumped together on databases: 1.1-1.4 g/cm^3 (https://echa.europa.eu/registration-dossier/-/registered-dossier/15300/4/5) The water content, hydrocarbon lengths etc will depend on so many factors, temp it was refined at, local or actual source of “tar” (pine, coal, peat etc)

It’s almost like we’re trying to generalise a cake mix, made by thousands of different bakers, it contains mostly the same stuff, but will cook totally different :)

Edit: But yes, you are correct that viscosity is greatly affected by particle/molecular size :D thanks for the correction :)