In the locations where there is frequent attempts by bunches of people to do the calling the thing, yotes have figured it out. That my be what is going on in your case at that location.
I've experienced this many times. In fact I can set up the caller in my back pasture behind the house a about 200 yards and will get several groups of yotes to howl at the same time.
They won't come to the typical mouth blown distress call. Frustrating!!!
I'm not talented enough to use a howler except for a locater. I don't understand their language.
I use a cobbled up VarmintAL Radio Shack 5W amplifier, metal horn speaker and iPod with the 16 and 20 minute sequences. These seem to have enough different sounds that seems to increase the success rate.
I'd mix up the call sounds a bit. But the more they are called and not shot the more they are educated.