Municipal wealth is not a mysterium fidei*

Cohen also referred to the “long battle cry of Chelmsford” to receive a larger share of state aid, pointing to Westford, which has a greater income per capita, greater property valuation per capita and the same school enrollment as Chelmsford, but is getting $6 million more in Chapter 70 funding. 

I know it's budget season, and I know that makes people tense, but it isn't as though these calculations and numbers are a great mystery or secret of the universe, as seems to be postulated above regarding Chelmsford.
The calculation of which community gets how much aid is the community wealth formula. Provided you've got Excel and can download 1.77MB, you can get the calculation for every community in the state from this page (the final option).
The FY15 community wealth calculations are based on the 2012 property taxes and the 2011 income taxes paid in each community. From that we see:

Property valuation (2012)
Chelmsford: $4,987,917,400
Westford: $4,000,201,300

Income tax (2011)
Chelmsford: $1,436,702,000
Westford: $1,149,597,000

So the answer is that Chelmsford has nearly a billon more dollars worth of property value and nearly three hundred million dollars more of income wealth than Westford does.

And that's why Westford gets more state aid.

I note that the town manager said "per capita" for both wealth and valuation. That isn't included in the formula, which operates on total community wealth, and I can't think of any reason why it would be. 

*mystery of faith