Open 0xr.space on a Meta Quest or an ARCore Android phone and press View in your space. On the Quest, pinch the model and hold still, then carry it to the floor, a table or a wall. A ring shows where it will land, teal on a floor or table and amber on a wall. Let go and it settles about 5 cm above a floor or table, or backs onto a wall facing the room. On a phone, touch the model and slide your finger to move it across the surfaces the phone has found.
Tables and walls are found only when the headset tells the browser about them, and a Quest browser often does not; the floor always works. With no surface in reach, the model stays where you let go of it. On the Quest, the model hides behind your hand only while a hand or controller is within about 40 cm of it, not behind furniture all the time.
The headset has not reported the table to the browser. Put it on the floor instead, or let go where you want it: it stays in the air there.
It rests about 5 cm off a floor or table on purpose, with its shadow beneath, so an estimated floor never swallows it.
No. Safari on iPhone and iPad offers no AR to a web page, so the model opens in the viewer on the screen.
No. Placement happens on the device, and the saved position stays in the browser.