asterisk users - Mar 2005 - Excessive indications tone levels (longish)

Setup:

POTS phone1 -> Panasonic Analog PBX -> Digium FXO - Asterisk1 - IAX2 ->
Asterisk2 - Digium FXS -> POTS phone2

I am attempting to balance the Digium FXO (shown above), analog audio 
levels using ztmonitor -v, which the information I have found means 
getting the TX and RX indicators to hit half scale on normal speech.

This results in an RX gain setting of 3.0 and TX gain of 0.0 and levels 
on both phones sound good to each party.

If however a call is placed as per the flow above and POTS phone2 is not 
answered, when POTS phone1 is hung up, the FXO on Asterisk 1 is never 
hung up, due to a failure of busy detect.

Looking at ztmonitor on the FXO, this is because the ringing tone on the 
TX side is going off the scale and after a few rings, appears on the RX 
side, overwhelming the congestion tone coming from the Panasonic when 
POTS phone 1 is hung up. I guess this is caused by the echo canceler 
being overloaded.

If the RX gain is reduced to 0.0, busydetect works about 80% of the time.

All of this is a long winded way of asking if there is somewhere in the 
code I can reduce the level of the indications tones (ringing, 
busy,congestion etc.)?

Given that the TX gain is set to 0.0 and these tones register off the 
scale, it would seem they are too high.

I am not a coder and some ploughing through indications.c shows mention 
of "vol" but I am not sure where this can be changed.

Any help would be much appreciated.

Regards,

Richard