You need to set the value of the second radio button with
.prop()
instead of val().
What I've also done in this solution is generalize it to handle whichever of the Tier1 radio buttons is selected. The path you started down would necessitate separate code for each possible selection, since you were getting and setting values down at the individual radio button level.
$('#<%=ChkSameAstier1.ClientID%>').on("click", function () {
if ($(this).is(":checked")) {
var tier1 = $('input[name=PFM]:checked').val();
$('input[name=PMFtier2][value=' + tier1 + ']').prop('checked', true);
}
});