i think this is almost correct but more so that asians are seen as overly conniving and hyper intelligent while fat people are seen as dull and easily gullible. so the fatphobia cancels out the racism and you have an asian thats dumb and unsexy categorically removing both the threatening and sexy aspects of orientalism and rendering the person an object of nothingness which is the american ideal. on top of the fact you mentioned which is that overweight asians are only ever viewed as objects of nothingness and typically portrayed as skinny rather than larger leading to a less overdetermined categorization of the person.