Easy answer
Well gone away for leave and thought you all would a solved this !
Flex, Couple of points.
As far as cost for training ( well actually cost for command courses as opposed to "training" goes it probably is not as simple as it looks. The FOs that are able to move right to left to do a command have some advantage under the current system. Those that change aircraft to do command have it a little harder. It is those FOs that may alter the appearance of cost per successful candidate. It is common sense that a command candidate will do better on a familiar airplane. So BBS in their wisdom decide to throw the FOs straight into the command course, knowing it is not the ideal situation but that if more than half pass then it is cheaper than checking them on to the airplane for 6 mos (or whatever)as an FO proir to a command course.
After someone fails the command course they then do 1 year or so in the right seat and viola pass the second time with very few exceptions. The down side of all of this is the toll it takes on the unsuccessfull candidates.
So for all we know BBS is quite happy to carry on this way as it is cheaper than giving two courses to every FO who must change aircraft for command. However the statistics show that there is still a high initial failure of candidates who attempt on the same aircraft, but that is a whole other problem and is offset by the above.
On another point, perfection is a long way from 55% ( exactly 45% away as a matter of fact). Most pilots realise that 100% pass rate is not a realistic goal, however a pass rate more in line with similar air carriers would be nice.
Not sure how you come up with a strategy for luck, as that is what makes the difference in most cases.
My 2 cents.