Greetings.
Yes, I know what you mean. I am playing Schubert's impromptu 4 right now, and in the trio sections one needs to search for the sound in the chords. Hand position is important. Make sure that your wrist are down and knucles supporting the fingers. Make sure that the fingers aren't flat. In order to be able to play softly a chord, first, dissect it. Play the lowest note of the chord only, in such a way that the key once depressed doesn't fully come back. Never let go of the key with the finger and as soon as it comes up, without fully doing so, depress it again, but make sure the sound is even. Then add another note of the chord. Make sure that the interval has no prevailing notes and that both notes are even. Then add more notes until the chord is gathered. Concerning the hand motion, the elbow needs not sack, but be sort of lifted to ensure good hand actions. With your arm, kind of make a slight pushing notion, as though you were shaking off drops of water without using the hand, but the arm. A slight pushing notion. That way, the arm supports the chords too. I hope that what I wrote made sense.