I'm afraid I was confusing two things: spoken dialect and the official written language.
Regarding the spoken languages, you are of course right: there was (and is) a dialectal continuum between Ripuarian (Cologne, Aachen, Jülich) and Limburgish (Limburg, Berg, the southern part of the Duchy of Kleve) dialects. There is not really a sharp border between these spoken dialects, but rather a gradual transition, and neighbouring "Ripuarian" and "Limburgish" dialects remain mutually intelligible. Generally, dialects Northwest of the Benrath Line - which is the line between light blue and light green on your first map - are classified as "Limburgish" and those southeast of that line as "Ripuarian", based on the usage of maken/machen (and in general, the consonant shift from "k" to "ch"). In reality, there is no such clear distinction. For example, my regional dialect, Velberter Platt, is just north of that border, thus a "Limburgish" dialect and we indeed use "maken" and not "machen". Nevertheless, our particular Platt for several historical reasons has strong influences from Kölsch, and both vocabulary and idiomatic expressions are much more similar to Kölsch than to the dialects of Dutch Limburg. The same is true for e.g. most dialects of Düsseldorf.
As for the shift northwards, I believe it exists in the spoken language to a certain extent, simply because of the cultural influence of Cologne and of the general tendency towards vocabulary and expressions that are more similar to Standard German. However, this is more a case of the Limburgish dialects adapting elements of Ripuarian dialects and Standard German, rather than them becoming Ripuarian dialects.
The dialects of Upper Gelre and most of the Duchy of Kleve (including the cities of Geldern and Kleve) are north of the Uerdingen line - the ik/ich or ek/ech border - and thus neither Limburgish nor Ripuarian, but Lower Franconian.
Regarding the written and official language, the situation is somewhat different: beginning in the 14th century, official, legal, and literary texts in what is today the southern border area between Germany, the Netherlands and Belgium replaced Latin by a peculiar common written language called "Meuse-Rhenish" (or Rhein-Maasländisch") by modern linguists. As far as I can tell, this area is shown roughly in your second map, however at the height of its usage, it did extend further south - this written form was used in documents in Jülich, Aachen, and even the northwestern part of the Archbishopric of Cologne (e.g. in Neuss). This written language, which was neither Dutch nor German, was slowly replaced by Standard German and Standard Dutch, probably due to influence of the Archbishopric of Cologne on the one and the United Provinces on the other hand - with the territories that remained mostly catholic and had catholic rulers (Cologne, Aachen, Jülich, Berg) adopting German and the protestant territories (Kleve, Mark, Gelre) adopting Dutch.
The area of written "Meuse-Rhenish" and later the areas of written Standard German and Standard Dutch do not correspond to the areas of the spoken dialects. Meuse-Rhenish was used in the Limburgish areas, but also in most of the Ripuarian area, and in the "Dutch" dialectal areas of Kleve and Upper Gelre. Usage of Standard Dutch and Standard German was determined by religious and political rather than dialectal borders.