Fast Att. Transfer

I’ve made and configured some (in that case - 3) PBXs for 3 offices of one organisation.(Asterisk 11)
office 1 have 100…199 numbers
office 2 have 200…299 numbers
office 3 have 300…399 numbers
All 3 connected via IAX
All working well? but…
some strange thing.
When we begin to transfer (attended) call to 1XX or 2XX numbers PBXs acts very fast, that means that
Party C( target of transfer) begins to ring immediately after pushing 3-d digit(without pushing #),
But when Party C in 3XX scope, we must press # or wait 3 sec(transferdigittimeout) to ring begin
Why it acts so? :open_mouth:
dialplans on all IPphones are similar and all includes [1-3]XX pattern
Thanks