Hhune Mausoleum secret wall

[Kumori]

Can't figure out how to open the wall. I know there's a pressure plate and inside the sarcophagus with a key and note that says, "Kneel with the weight of all you value at his feet, and he will reveal himself."

Thing's I've tried:
Standing on the plate
Putting stuff on top of plate (including over 17k gold)
Having someone with excessive weight on them stand on top of the plate, up to 240 lbs

All other pressure plates so far just require something to be on top of it and you'll see/hear a click.

[xInSt*r]

There is one plate that can be seen with high enough perception. Have all 4 members crouch onto that plate and the wall will be revealed.