Soft palm strike?
There is a soft principle apllied in WC but there isnt something called a soft palm strike which differs from a normal pal strike.
Its just means that you have to stay relaxed while you are hitting, training and only tense at the last moment and relax again as soon as that moment is over.
Through chi say (sticky hands( you learns to allow your opponent to push you, but only for the purpose of redirecting the motion onto him. Think of it as a spring board that allowes some compression but jumps out at the first opportunity.
Hope this helps with your question.