fax machine behind a spa8000 unable to send faxes using E1 with Ec card

Hi there
we have 2 Scenario:
fax machine spa8000 trixbox v2.6.2.3 rhino E1 card with EC fastweb (italian telco) pri
fax machine spa8000 trixbox v2.6.2.3 sip trunk with italian voip provider

when we send fax using sip trunk with voip provider, we have no issue
when we use land line outbound route we have high loss rate (98% of faxes are lost)

further, we were able to send faxes using traditional pbx and E1-pri line

so, spa8000 and E1 pri line are not an issue, we think we should fine tuning Rhino E1 card configuration

this is zapata.conf

; Zapata telephony interface
;
[channels]

language=it
context=from-zaptel
signalling=pri_cpe
switchtype=euroisdn
rxwink=300
;loadzone=it
;defaultzone=it

;pridialplan=national
;pridialplan=local
;pridialplan=dynamic
pridialplan=unknown

;prilocaldialplan=local
;prilocaldialplan=national
;prilocaldialplan=dynamic
prilocaldialplan=unknown

nationalprefix=0
internationalprefix=00
;localprefix=0
unknownprefix=0

usecallerid=yes
hidecallerid=no

callwaiting=yes

;https://www.trixbox.org/forums/trixbox-forums/help/zaptel-dropping-calls-isdn-pri-major-update-sorry-urgent
;usecallingpres=no
;callprogress=no

usecallerid=yes
hidecallerid=no
callwaiting=yes
usecallingpres=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
callreturn=yes

;echocancel=yes
echocancel=no
echocancelwhenbridged=no
echotraining=no

rxgain=-5.0
txgain=-5.0

callgroup=9
pickupgroup=9

immediate=no
callerid=asreceived

group=0
channel => 1-15,17-31 ;for E1

;faxdetect=both
;faxdetect=incoming
;faxdetect=outgoing
;faxdetect=no
;Include genzaptelconf configs
#include zapata-auto.conf
; group=1
;Include AMP configs
#include zapata_additional.conf

zapata_additional.conf and zapata-auto.conf are empty.

voip:/etc # cat zaptel.conf
# Autogenerated by /usr/sbin/zapconf on Tue Nov 25 04:49:50 2008 -- do not hand edit
# Zaptel Configuration File
#
# This file is parsed by the Zaptel Configurator, ztcfg
#
# Span 1: R1T1/0 "Rhino R1T1 E1/PRA Card 0" (MASTER)
span=1,1,0,ccs,hdb3,crc4
bchan=1-15,17-31
dchan=16
loadzone = it
defaultzone = it

alaw=1-31

relevant kernel modules:
lsmod
r1t1 102468 31
zaptel 187908 65 r1t1
oslec 13848 1 zaptel
crc_ccitt 6337 1 zaptel

any help is very apreciated