I mean when you are actually painting the hole on the landscape using the brush. If you check “use target value”, then instead of painting or erasing (1 or 0), the paint brush will apply the selected value.
So try changing that target value to 0.1 and set tool strength to 1 just to make sure its being applied enough. Then try re-painting your foundation hole again with that value. Also try values up to 0.33. Anything over 0.33 will probably make the hole disappear.