Fetch value from a different entity (content type) to include in math in Views

I've searched extensively for a solution to this but can't find any, though I think it should be an obvious need.

I have a View that works fine, displaying product information and prices in a table from an entityForm's submissions. I have another entityForm submission that has several individual fields storing default tax rates. I want to display a price-including-tax column in my View but can't seem to pull in the default tax field values from the other entityForm to use in a math expression to generate this +tax column. I can create a tax rate field column (I can choose the tax rate fields in my view's add-field list) and extend my filter to include that entityForm's submissions but the column is always blank. I suspect because it's not associated with the other elements of the record in the row.

Any suggestions as to how I can bring in these values and apply them in a math expression column?

I'm Using D7.5 and Views 3