SKILL ipcBeginProcess() vs sh()

Hi there,
I'm trying to run Calibre within Cadence environment using SKILL functions. So far I have two ways to do it. Both of which work and I got the final goal. However, running Calibre with the following code:
Method 1)
CommandLine="calibre -drc -hier _myDrcSetup_"
ipcP=ipcBeginProcess(CommandLine) ipcWait(ipcP)

takes around 25 minutes to complete the DRC run. (*Note: I get no log from Calibre on my terminal even so I use ipcBeginProcess with no option). On the same layout, using the following code:
Method 2)
CommandLine="calibre -drc -hier _myDrcSetup_"
sh(CommandLine)

I got the results in less than 5 minutes.I got all the log information on my terminal while Calibre is running.
My question is:
Why ipcBeginProcess takes so much more time ? I am more willing to use that because it seems a more elegant way to handle the task but taking that much longer is really frustrating and unacceptable. Also I am a bit concern that sh() can somehow mess up the whole flow of the script. And second of all, why ipcBeginProcess does not produce any Calibre log info in the parent terminal window?