OK, you use the IP command and SC command to make the HP-GL/2 coordinate system congruent to the PCL coordinate system.
Attached is 'hpgl.txt' which has a complete PCL/HP-GL/2 initialization.
Read the manual for an explanation of the commands. This is for letter size paper and would change for other paper sizes.
So either <esc>*p272x1335Y or PA272,1335; will place the CAP on the same pixel on both the PCL and HP-GL/2 page.
Holler if you have any questions.
jim