So if palace get 60 in the league and cardiff get 82
Result is Vc Palace 88, Cardiff 88 - back bet wins bf Palace 87, Cardiff 89 - lay bet wins
If palace win vc hcap by 1 or 2 points over cardiff, hull, middlesborough and others in second you win both. If palace tie at vc with one of them you get half the back and win the lay. If palace win by 3 points with one of them you win the back but only lose half the lay.
Summary- for some teams it is a straight arb. for some teams you could win both sides of the bet (e.g. cardiff, hull, middlesborugh,barnsley etc.) for some teams you could win one side and lose only half on the other (e.g cardiff etc.), for other teams it is only an arb (huddersfield etc.) for one team the potential to go wrong is burnley if these two are first and second by 1 point.
I reckon it is a small arb with about a 1 in chance of making a nice profit.