Penetrability doesn't affect format
No evidence that cognitive penetrability affects the depictive aspects of the imagery format itself, as opposed to specific contents within the format—ie images of specific objects or patterns. The debate's about format—the type of code—not content.
"The debate hinges on the distinction between the format versus the content of images: The format is the type of code, whereas the content is the information conveyed. The same content can be conveyed using many different formats; for example, the information in this sentence (i.e., the content) could be conveyed using the dots and dashes of Morse code, using the words and grammar of French, speaking English aloud, and so on (each of which is a different format). The debate focuses on the format of the representations that give rise to the experience of imagery, with one side arguing that at least some of these representations preserve key aspects of pictures (e.g., Kosslyn, 1980) and the other arguing that these representations are in no sense pictorial but rather rely on abstract symbols of the sort used in language (e.g., Pylyshyn, 1973, 2002, 2003)."
Kosslyn and Thompson (2003, p.723).