The concept of retardation is usually applied successfully for the description of transport in two-phase systems of different kind with one moving and one stagnant phase. It simplifies understanding the multitude of processes in the two phases. Retardation factors can be derived from measurements and also mathematically from basic transport equations in the single phases, and thus form a link between practice and theory. The author recently presented a generalization of the theoretical derivations for systems with two moving and/or diffusive phases, in which so called R-factors were introduced. Like retardation factors, R-factors reduce the complexity of the description of a two-phase system. Here conditions are examined in detail under which the generalized R-factor approach is applicable. A demonstration example shows steady states depending on phase dependent reaction rates. A final example application demonstrates how the approach works interpreting real world data.