Native English speaker here - for me, I have to really listen for the 'rasp' and 'rattle' in the throat of ח and כ. It seems to me ה is more of what us English speakers would think of the classic 'H' sound - like you're freely breathing out - such as in 'hello', 'Harvey', 'hoppy'. We have to train our ear to hear the difference, because we don't have the sounds of כ or ח in our native language, so we tend to 'hear' it as indistinct from ה. What worked for me was to listen carefully to the Duolingo recordings that had this sound, to make myself better at identifying it. Hope that's useful!