Sitting a part on the ground

Use Place On with the Base input left unwired. It measures the part and seats it on its own underside, at any size.

Do not type the lift by hand. A typed number is exact at the size you calibrated it for and wrong at every other size, and it fails silently: the part floats, nothing warns, and the graph still evaluates. Measured across a family of parts, one scaled to 0.7 floated a fifth of its own length above where it belonged.

There is a second trap, and it catches people who have already done the first part right. A measured seat is only correct while the underside is flat. Displace or roughen a part after seating it and the contact collapses to a single point: the part visibly floats while its measured bottom still reports a sensible number.

Three ways out, in the order to try them.

Seat last, after everything that moves the bottom face. This is usually the whole fix.

Or mask the displacement off the bottom face, so the contact patch never moves.

Or slice the base flat afterwards, which makes the measured bottom the true contact patch again.

A bounding box is not a test for whether a part is sitting on something. It can report a perfectly sensible number for a part balancing on one corner.