The only program I ever came across that had a WIDE, and I mean wide variety of HPGL post variables was/is Signlab. Thats probably because back in the day, there were tons of machines using hpgl.
About the only help you could get from a Signlab user however is a back and forth attempt to first establish a good test sequence/drawing where specific sized entities in specific locations and subsequently specific cutting order are understood. Then the posted code output could be tested for proper operation and finally, one could attempt to make a test drawing/toolpath that would allow a person to see ALL of the potential variables for that specific control.
I know what your going thru because I dealt with an MCam MT22 for some time..... it sucks compared to ANY version of G-code, and I would RETROFIT a different control in a heartbeat. Well, not just any control though... I'd definitely use Flashcut !
Usually, its not the x,y locations of the hpgl, its the many penup, pendown, Rapid rate, cut rate, acceleration subsets that any one particular control COULD use. Each different company did what they felt like, rather than attempt an industry standard for those subsets.
MultiCam was never one to publish much of that info.... my research led me to Extratech..... the control the Mcams were using at that time.
ExtraTech Corporation - Motion Control Solutions
While back in the day, I did attempt to talk to them, I do not recall it going anywhere other than to contact Multicam.
HPGL was used initially because all Cad programs were intended to "PLOT" to a printer.... wasn't a bad idea necessarily. We would all like to have native G-code output directly from Cad wouldn't we !