Rigidbody behaves different from particles

I came across this weird behaviour when testing a simple physics calculation in Blender 3.2.0.

Grav.blend (1.2 MB)
In the attached file, the particles and the cube are supposed to have the same mass, 1kg. The forcefield has 9.81 (N, I assume?) with a gravitational falloff.
Neither the cube nor the particles have any drag or airflow applied.
As a result, objects with mass 1kg should not move if starting out in a stable position 1m above the force field. However, the particles behave according to this while the cube moves as if it had a higher mass.

I set the substep of the rigid body world to 1 with a solver iteration of 100, higher values make it look more stable, but I need to manipulate the simulations speed to 1/substep for it to look realistic and even then the cube still behaves flawed.

Am I doing something very wrong?
Is this intended behaviour or a limitation with forcefields and rigidbodies?

I just tried your file and I notice that if I delete the force field, the particles fall at a different rate than the rigid body. It seems the 2 physics systems have a different behavior in general.