Tim,
I do not think that you read this document very carefully. If you had, you would have seen that the answer supervision (setting tonebasedsupervision to 2 or 3) will only work correctly if the signaling is loop start. You have this set for loop start with reverse battery. Therefore, as discussed in the document, the tenor will expect the PSTN connection to send a battery reversal for both answer and disconnect. I doubt that is what is happening.
Change the signaling to loop start only, set the answer delay to 120.
Please re-read the document as I am pretty sure it does talk about all of this.