Merging functional coverage problem

Hi,
i am facing a problem with merging functional coverage of two different testcases.

Here am using irun command to ganarate functional coverage of individual test case

COVERAGE : irun -coverage functional cov -covworkdir cov_work -covscope scope -covtest test -covoverwrite -access +rw -f flist

and ICCR to merge all functional coverage reports and genarate merged functional reports

iccr -batch
set_dut_modules top
merge -functional cov_work/scope/* -output merged_all
load_test cov_work/scope/merged_all
view

when i run these commands it does not showing any errors but the merging report is showing only the first testcase functional report.

Please let me know your inputs.

Thanks & regards,
venkatesh

before merging run the fallowing command.
set_merge -union
this is not the right platform to discuss tool specific things.