Some troubles with SSAO

[issimissimo]

Hello, I'm trying to use SSAO but I have some troubles and / or questions:

1 - I'm initializing it this way
const ssao = new POSTPROCESSING.SSAOEffect(camera, { blendFunction: BlendFunction.MULTIPLY, radius: 0.5, samples: 24, bias: 0, // other properties });
composer.addPass(new POSTPROCESSING.EffectPass(camera, ssao));

but all the ssao option values are the default ones (it's not using my option values).
Maybe I'm using the wrong syntax?

2 - Since my options don't work in the constructor, I manually set them later:
ssao.radius = 0.5; ssao.samples = 24
but I don't know how to set the bias (ssao.bias is undefined)

3 - so, I forget the bias and I play with other parameters, but the SSAO effect is barely visible (no matter the parameters I use)
Here below the comparison (without and with SSAO)

The plane is 2x2m (so the monkey is about 1m)
The SSAO has has a very very little effect on the monkey, and no effect at all on the plane (at least I think I should see some AO where the monkey touch the plane...)

I'd really appreciate some help to understand what is going on, or an example sandox.
Many thanks!