Does Agar Agar expand in the stomach if not diluted enough?
Assuming that you are worried about the expansion rate in the stomach from having an insufficient ratio of water to agar during digestion, a quick search came up with the following results from wikipedia (https://en.wikipedia.org/wiki/Agar):


  Agar-agar is approximately 80% fiber, so it can serve as an intestinal regulator. Its bulking quality has been behind fad diets in Asia, for example the kanten (the Japanese word for agar-agar[3]) diet. Once ingested, kanten triples in size and absorbs water. This results in the consumers feeling fuller. This diet has recently received some press coverage in the United States as well. The diet has shown promise in obesity studies.


The same Agar used in culinary dishes is the same one used in laboratories for testing.  Resistance to high temperature (melting point is 85 °C) makes Agar ideal for studies that need an environment to mimic human body temperature.  This means that Agar will not melt in the body once digested.

Melting Agar is also not the same as denaturing Agar.  The act of melting it to form and then cooling to set does not change the structure and properties of Agar.  Just like how ice melts into water and you can freeze again while also being able to reverse the process at any time, you can do the same with Agar just at a different temperature.  Since the Agar has the same properties as before melting, this does not keep it from expanding when exposed to water.

To add to this: Just because your body does not get hot enough to melt agar, that does not mean the bacteria in your intestine won't break it down into smaller molecules and denature the Agar to aid in digestion.  Source: https://www.ayurtimes.com/agar-agar-kanten/