O que realmente está acontecendo com essa busca?

SELECT AddressTypeID, FullAddress
FROM dbo.Addresses
WHERE CustomerID = 783
AND AddressTypeID IN (2,4,5);

CREATE INDEX ixIdealIndex 
ON dbo.Addresses (CustomerID, AddressTypeID)
INCLUDE (FullAddress);

CREATE TABLE dbo.Addresses (
  AddressID INT IDENTITY(1,1) PRIMARY KEY,
  CustomerID INT NOT NULL,
  AddressTypeID INT NOT NULL,
  FullAddress NVARCHAR(MAX) NOT NULL,
  SomeOtherColumn DATE NULL
);

WITH nums AS (
    SELECT row_number() OVER (ORDER BY (SELECT 1)) AS num
    FROM master..spt_values
)
INSERT dbo.Addresses (CustomerID, AddressTypeID, FullAddress)
SELECT num AS CustomerID, 1 AS AddressTypeID, N'Some sample text for the address' AS FullAddress
FROM nums
UNION ALL
SELECT num AS CustomerID, 2 AS AddressTypeID, N'Some sample text for the address' AS FullAddress
FROM nums
WHERE num % 10 < 8
UNION ALL
SELECT num AS CustomerID, 3 AS AddressTypeID, N'Some sample text for the address' AS FullAddress
FROM nums
WHERE num % 10 < 6
UNION ALL
SELECT num AS CustomerID, 4 AS AddressTypeID, N'Some sample text for the address' AS FullAddress
FROM nums
WHERE num % 10 < 4
UNION ALL
SELECT num AS CustomerID, 5 AS AddressTypeID, N'Some sample text for the address' AS FullAddress
FROM nums
WHERE num % 10 < 2
;