Perhaps Caa should create a new term " Minimum cruise altitude".
I always taught 10nm either side of track, highest hill plus 300 feet, plus 500 feet or highest structure above that, plus 500 feet to determine a minimum exceptable cruise altitude should the cloud base drop. Also use this as a go/no go on cloud base forecast.
Draw three parallel lines onto a sheet of acetate, each 10nm apart and use as a overlay when flight planning.
Using the MEF can also be a bit restrictive should there be a high obstruction in the "corner of the box".