https://www.academia.edu/30823402/Raumstrukturen_im_Niederdeutschen_Eine_Re_Analyse_der_Wenkerdaten has a statistically substantiated map of Germany on page 19. There is 3.1 for the Kleve and Duisburg districts, but the Viersen and Mettmann districts and also the city of Düsseldorf have 3.2. On page 22 it reads for 3.1 Niederfränkisch and for 3.2 Mittelfränkisch. Southern Low Franconian indeed has Middle Franconian components such as tone language. The problem of any transitional group of dialects such as Southern Low Franconian is that the division is arbitrary, one study is not enough for a complete restructuring of the division of the dialects. The method of Daan 1969 is based on opinions of the general population. Although due to the political demarcation of the Limburg area into Dutch (after the formation of the Kingdom of the United Netherlands) and German (after the annexation of the eastern part to the Kingdom of Prussia), there is a strong influence of the Dutch and German literary language respectively in them, mutual understanding on both sides of the border remains in some cases.
