The formula for points does not represent a set number of calories; the intention was that one point would be equivalent to approx. 50 calories, but there is a great variation.
In wikipedia, under Weight Watchers, the various formulas are explained. One quote from that article is very telling: "The range of calories for one PointsPlus point is approximately in the range of 35-45 calories, in contrast one Point had a broader range of approximately 25-80 calories. " en.wikipedia.org/wiki/Weight_Watchers
The momentum points formula gives a penalty for eating fat and a large reward for eating fiber. The new formula for Points Plus does not penalize fat, and the reward for eating fiber is much smaller than for the points formula.
I think it may be beneficial for you to use most of your weekly allowance to compensate this low calorie count when counting your points. The Momentum program is an excellent program. You know by experience, and so do I, that it will allow you to lose all the excess weight that you want to lose.
You may be interested in the Wendie Plan that was created by a WW member to maximize weight loss by using the weekly allowance. www.sparkpeople.com/myspark/groups_individ
Personally, I have recently (6 weeks) switched to Points Plus and I am still trying to adjust. From tracking both calories and Points Plus for a few of those weeks, I believe that my daily allowance plus weekly allowance corresponds very closely to the calorie range recommended by SP. Each point+ in my case seems to be worth approx. 47 calories. I do not recommend that you switch to Points+ -- it is not necessary; the Momentum program is just as good.
I wish you great success in this endeavour.