I have a telco that is returning a busy instead of a loop drop, is there a setting in the Sv8100 that I my not be aware of that can use that to disconnect?

Make the carrier send the correct disconnect or find a new carrier.

14-02-18 Busy Tone Detection on Talking

that's what I was thinking, didn't seem t work. Think I have it working well enough by having the AA hang up on no entry.

and that is when customer says "never had any issue on the mitel"

Look at 14-02-09 and you probably will need to turn off detect disconnect (possibly) you might also have to adjust 14-02-19 and 20 depending on the busy generated. Disconnect is a carrier thing, sometimes we have to adjust timing but it's an industry standard despite making a Mitel detect busy. FWIW you usually have to reset the trunk card for settings to take place.

Also the vital part of busy tone detect lives in PRG 80.04 BT for Trunks. This sets the tone cadence durations and pulse counts.