x100p clone on UK residential extension

Hi all,
been tinkering with this one for a while and wanted to get opinions, suggestions from the folks here.
I’m on a standard UK BT POTS line, with normal BT phones plugged in, and my asterisk server with its x100p card.

What I want is that anyone can answer the incoming calls, either the extensions directly wired into the bt sockets, or asterisk.
The problem i’m having is asterisk doesn’t seem to be able to detect that other extensions are answering the bt line.
Is there a way of letting asterisk detect this?

Current settings i’m using are:

zapata.conf

language=en
context=from-pstn
signalling=fxs_ks
channel=>1
usedistinctiveringdetection=no
usecallerid=yes
cidsignalling=v23
cidstart=usehist
ukcallerid=yes
hidecallerid=no
callwaiting=no
usecallingpres=yes
callwaitingcallerid=no
threewaycalling=no
transfer=no
canpark=no
cancallforward=no
callreturn=no
echocancel=yes
echocancelwhenbridged=yes
rxgain=0.0
txgain=0.0
group=1
callgroup=1
pickupgroup=1

immediate=no
busydetect=yes
busycount=4
answeronpolarityswitch=yes
hanguponpolarityswitch=yes
callprogress=yes
progzone=uk

Thanks in advance for any tips to try!

My impression is: not with X100P. I’m in North America and I have same issue, so reported other people in the forum.