Maay is a different Somali language like how Neapolitan is a separate language but still one of the native Italian languages. These are basically divergent dialects. Sometimes dialects turn into languages just because of other socio-political factors. I think af-Maay and af-Maxaa are less intelligible than Swedish and Norwegian, for example. Sometimes you even have wider dialect differences within a country where some regions of that country are closer to a neighbouring country that speaks a language that is classified as linguistically separate. One needs to note that, just because Swedish and Norwegian are similar, and we can understand each other, they still have their differences that some might structurally regard as divergent enough for a separate linguistic classification placement.
Af Maay is a Somali macro-dialect but by common standards a language.
Here is a lexicostatistical relationship between the various dialect languages:
To get a sense of an understanding, these are the Maay dialects:
As you can see, certain dialects that are af-Maxaa have a stronger relationship with af-Maay dialects than other Maxaa to Maay. This is because of regionality and historical influence. Now, the thing is, the lexicostatistical analysis might not mean a total 1:1 relationship with intelligibility. Nevertheless, I think if you share a lot of cognates, that usually either means shared genetic roots that are more recent, moreover, it probably means fewer deviations in other linguistic dimensions dealing with understanding across related dialects. That is my reasoning, at least.
These are af-Maxaa regional dialects:
You can see that Maxaa, which is standard Somali is basically very similar across the board.
Studies have shown that standard Somali speakers increase their understanding of af-Maay through contact. Meaning naturally we don't really comprehend things comprehensively. However one can easily familiarize oneself through contact, without necessarily speaking or studying the language.