Wick
I only get on the board once a day (if lucky) so i'm just getting back to answer. Our experience for a long, long time was just the opposite. We only seemed to get the coyotes that answered. If we didn't get an answer we were discouraged. Then we figured out we were more patient when we knew coyotes were close. BINGO Change in success when howling!!
Be prepared to stay an hour if you hear them. We usually answer them back at least once, maybe more if things seem to not be progressing. We will certainly add distress sounds as time goes along, but only after being convinced they aren't coming without the "help".
As an example (granted an extreme example), we once sat for 2.5 hours communicating with a pack. They were close, but in cover and we just had the feeling that they were going to come in. They always answered so we knew they hadn't left the area. Finally we called in 5 (tried distress but it was howls at beginning and end) and got 2. Then called 2 back in and got another. Probably should have had more, but it was 0 degrees and we were so cold we were shaking by the time they gave us our first shot.
Thought i could share some first hand experience from over 25 years of calling.
Doc