Arcade monitor video tweak help?

 Hello all,
 I'm helping a friend setup  their Advmame / Advmenu cabinet with an old Sega Astrocity 29"  cabinet.  We have everything setup and running great with WinME,  JPac, G400 and an SB Live, except for the video.
  
 The screen  image is a little too high, so that the sync rolls over on the top inch  or so of the display.  This happens even with the hardware  controls on the monitor all the way down.  We've gone into Advcfg  and moved the image down and saved the rc file, but Advmenu doesn't  seem to move it's position down.  What video mode / res does  Advmenu use by default?  Ultimately we'd like to adjust the video  to display lower, to compensate for the monitor being a bit off if it's  possible.
  
  Any help would be greatly appreciated!
  
  Thanks,
  Thomas
  

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