my understanding is not so much altitude as the density of what’s pulling you, as in the ground below you. like if your at the top of a granite mountain it may have more pull than if you’re on the ocean. if you search for gravity anomaly maps you can see what I’m getting at. of course the farther you are from something the less pull it has though so I get your altitude point but unless you’re in a hot air balloon weighing rice I don’t know how altitude would matter. not that there is a big enough difference for weight vs mass to ever matter with rice.