I'm looking at booking a return leg from Singapore for which there is only full fare economy available booking in Y which brings the return ticket cost to RM2578.

Booking Business Basic (D) would make the round trip RM6 more expensive at RM2584.

Do MAS offer automatic upgrade for full fare economy Y to Business if there is room on the seat? Are check-in agents empowered to do this, even if they inclined to do so? Is this a perk formally/informally offered to Gold or Platinum Enrich members?

Perhaps, the MHUpgrade price offered changes depending on the differential between economy price paid and discount Busienss?

This would be common in North America and it's to circumvent employers 'economy only' travel policy even when an upgrade to Business would cost RM6.