We've discussed this subject before, and one of the problems is that stroke indices are used in different ways.
In countries where Stableford play is common [the UK and Australia], the stroke index should be correlated with the difficulty of the hole.
In a match play scenario, it's more important for the strokes to be spaced relatively evenly, and hole difficulty doesn't matter so much. In fact, in Australia, some scorecards show a separate stroke index for medal play and match play -- and the match play one has the strokes evenly spaced out [first four given on holes 8, 12, 4 and 16], completely regardless to what sort of hole it is. I first noticed this on a course where the #1 stroke hole was a 170 yard par 3!
In truth, for match play, it really doesn't matter where the strokes fall. If you got a stroke on that par 3, and won that hole, you'd probably have lost the long par-4 before it that you thought the stroke hole should have been.