The Artscroll siddur has 3 one line congregational responses after parts of the tiskabel kaddish (e.g., kabayl brachamim uv'ratzon es tefilasanu). The siddur says these lines are said by the congregation. There is no indication that the responses are optional or said by some. I have never heard them said and they do not appear in other major siddurim (Birnbaum, Sacks, Metzuda). What is the source of these responses and why does Artscroll give such strong direction that they be said?