Well I've just checked and I can boot from the HDD on my CSPPC with the CDrom on the 1st IDE lead position set as Master OR with the CDrom on the 2nd IDE lead position set as Slave.
But to boot into OS4 BootFloppy & OS4 CD, the CDrom drive must be on the 1st IDE lead position and set as Master.
(If the CDrom drive is on 2nd IDE lead position and correctly set as Slave, I get "Please insert volume AmigaOS 4.0 Install CD in any drive" when booting into BootFloppy & OS4 CD)