Well, here's your tutorial.
What you are describing is called GLARE.
By definition, GLARE happens when ALL LINES RINGING IN and ALL LINES DIALING OUT are in the same pool. - SC's used to ALWAYS set them up that way...
There's a couple of good ways to fix that.
BEST - Have some lines dedicated to ONLY OUT GOING, and not part of your incomming hunt, and move them to your outgoing pool.
ALMOST AS GOOD (Without having to call the service provider) - CREATE 5 DIFFERENT POOLS to correct this problem, and set up ars to accomodate it.
Pool 1 would be the 70 pool with the LAST 4 LINES of your hunt group in it, lines 816-819 as you indicated. Pool 890 would have the NEST TO THE LAST 4 lines in the hunt group lines 812-815. Pool 891, lines 808-811. Pool 892 lines 804-807 and last, Pool 893 would have 801-803.
Then set ARS up to select pool 79, then 890, then 891, then 892, then 893.
HERE'S WHY - Lines in pools are used in a "CIRCULAR" hunt. So, if youy have ALL 19 LINES in the SAME OUTGOING POOL, which is also the INCOMING HUNT GROUP, you are going to have GLARE.
Let's say you set it up the way I described.
Now, the only time first 3 lines would be accesssed would be if all 16 others are in use. In fact the only way any of the first 7 lines could be accessed would be only after all 12 other lines were in use. And so on...
This would pretty much eliminate the cause of GLARE.
Let us know how this works out....