Interesting, you're getting a lot more density than I have been with my retro 320 shots. Maybe I need to mix up a higher contrast developer and try that.
You could ask the same about most conventional B/W films. HP5 is a film that I have been using for decades. It probably would handle this situation better... I only wanted to see how this film would respond to the situation, and the two developers.
They'll give you an answer similar to this (Ai overview):
"Foma Retropan 320 Soft is a black-and-white negative film ideal for achieving a classic "retro," romantic, or cinematic look, characterized by low contrast, wide tonal range, and noticeable, sharp grain. It excels at portraiture, atmospheric landscapes, still life, and architecture, especially when developed with the dedicated Foma Retro Special Developer to manage its unique contrast characteristics."