Obese people have faster drug clearance and higher blood volume. Clearance is the time it takes for a drug to be removed from the blood. Basically drugs in obese people wear off faster so they need to take more to maintain desired drug levels. Now, I am unsure if faster drug clearance makes any difference with SN, which is a very strong oxidizer that changes hemoglobin into methemoglobin. The body is able to turn methemoglobin back into hemoglobin, but this process is different than the process used to clear drugs like caffeine out of the blood. So should an obese person take more SN based on drug clearance? There isn't enough data on SN to make a conclusion. Now blood volume. An adult male who weighs 180 pounds has approximately 5.5 liters of blood and an adult male who weighs 300 pounds has approximately 7.2 liters of blood. That's an extra 1.7 liters of blood which is an increase of about 30%. If you add 30% more SN then the total SN would be 32.5 grams. Now, should someone take extra SN based on their blood volume? I feel this is a personal choice. Sometimes less is more, especially if more means you vomit quicker. 25 grams is already several times the lethal dose for an average adult so I'd say the choice is up to the individual.
For anyone interested you can find out your blood volume by using the calculator I used here:
https://www.omnicalculator.com/health/blood-volume