I wrote two assertion in same way, but one of them is covered, but other does not.
(a_signal == 16'h48) ##[1:6] $fell(c_signal) |=> it is ok
(a_signal == 16'h28) ##[1:6] $fell(c_signal) |=> does not work
I observed test's graphic that two cases (16'h48 and 16'h28) occur. but the one of assertion doesnt cover.