Estimating monthly values from table using start date/end date

Hi MT

I think this might be getting close

Table = 
GROUPBY(
    FILTER(
        CROSSJOIN(
            -- Create and on the fly calendar table with a month column
            ADDCOLUMNS(
                CALENDARAUTO(),
                "Month",FORMAT([Date],"MMM-YY")
                ),
           -- Add a column to our base table that adds an average daily value
            ADDCOLUMNS(
                'Table1',
                        "Averate Usage Per Day",
                        DIVIDE(
                                'Table1'[Usage Value],
                                DATEDIFF(
                                    'Table1'[Start Date],
                                    'Table1'[End Date],DAY
                                        )
                                )
                            )
                            ),
        'Table1'[Start Date] <= [Date] && 
        'Table1'[End Date] >= [Date]
        ),
        -- Perform the actual grouping here --
        -- So Group by --
        [Identifier],
        [Month],
        -- Now sum up the Average daily usage for the above groupings --
        "Usage Value", SUMX(
                            CURRENTGROUP(),
                            [Averate Usage Per Day]
                            )
        )

If I run this over your sample data I get the following result