I've tried out some things; seems to me that the ECO signal comes on when there is no acceleration aka steady speed. Even at 100+ mph . Lol.
Yes, even when the ECO light is on it does not mean the MDS is active it merely means that the engine is under a certain load percentage and that the engine RPMs are between 1200 and 2800. MDS cannot activate above 80 MPH IIRC.