Originally Posted by
d3vski
with my usual carrier British airways on the lhr-bom route
the fares (all discounted) usually break down like this :
Y = £350
Y+ = £650
J = £1600
F = £3500
y to j = 5 x difference
y to f = 10 x difference
j to f = 2x diffrence
Obviously, you are using Y, J and F loosely and not as a specific fare bases. You are also confusing cabin designations with fare bases. One can't compare an economy class fare with business class or first class haphazardly. J is full fare business and Y is full fare economy. What you are calling J is not J, as J is a full fare. There is a world traveller plus, but no Y+ on BA.
Looks like you have taken the lowest coach fare and comparing it to any odd fare in other cabins. Cheapest coach fares (cheapest World Traveller) earn only 25% miles and no tier points while all World Traveller Plus fares earn 125% miles and tier points. You need to compare fares with similar restrictions