The refining margin for very-low sulphur fuel oil (VLSFO) edged slightly higher on Monday after its recent tumble to more than two-year lows. The front-month crack spread for 0.5% VLSFO closed higher at a premium of $6.72 a barrel by 0830 GMT. Meanwhile, cash differential for 0.5% was pegged at a discount of $2.40 a …