If you turn on Vertical Momentum (or Vertical + Horizontal) the dash operates more like the one in Megaman X. You can also do more fine-grained tweaks with the Attach Script to Platformer+ State event.
As a note, GBStudio 4.2 (which just came out) added Platformer+ as a default part of the engine. If you upgrade to that version, you'll probably need to delete the plugin.