I've tried to tilt my dulcimer up as described here. The instrument does resonate much better that way but certain fingerings are also more challenging. Just have to stick with it I guess. Somewhere between the angle of the tilt and how much you point the dulcimer away from you seems to be the key.
Someone mentioned putting it on a hard surface like a table top. I'll have to try that. I'm a telephone tech of 30 years. Putting the phone (an old phone with REAL bells) on a hard surface was a good cure for customers who were hard of hearing and often made the difference in hearing the phone or not hearing the phone when it rang.