You must consider the Odds of the rest of the Field.

Picture that the Favourite was BlackCaviar.
Your $1.50 a place horse has virtually zero chance of winning.
Therefore the whole 66% place chance is divided up between 2nd and 3rd position.

If your horse was substantially better than the rest of the also rans, then it could be divided up as 50% and 16%
If it were of equal ability of say 2 other runners, then it could be divided as perhaps 33% and 33%.