I have different setting for the type of wood.  Have slowed the speed and increased the intensity based on hardness.

Nevertheless I tend to rely on passes more so...  I usually engrave with a double pass unless it's just for markup.  The secret is to not move the piece after engraving, check it out and then apply more passes.
If needed, determine the depth after 1 or 2 passes, adjust depth and maybe repeat passes.

If your first cut is too short... Take the second cut from the longer end... LBD