How to search a PostCode in a Radius using sql server 2008 GeoGraphy

Question

I followed this blog http://blogs.lessthandot.com/index.php/DataMgmt/DataDesign/sql-server-2008-proximity-search-with-th and did everything which was guided and I am glad things went fine, my table definition is mentioned below and the query I am executing is also mentioned below.

I am using CodePointData data which is downloadable from https://www.ordnancesurvey.co.uk/opendatadownload/products.html

USE [TestDb] GO

/****** Object:  Table [dbo].[PostCode]    Script Date: 08/23/2012 05:32:05 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[PostCode](
    [PostCode] [nvarchar](10) NOT NULL,
    [Coordinates] [geography] NOT NULL,
    [Coordinates1] [geography] NULL,
 CONSTRAINT [PK_PostCode] PRIMARY KEY CLUSTERED
(
    [PostCode] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON)

ON [PRIMARY] ) ON [PRIMARY]

GO

SELECT distinct(left(h.postcode,4))
from postcode g
join postcode h on g.postcode <> h.postcode
and g.postcode ='IG1 4LF'
and h.postcode <> 'IG1 4LF'
Where g.coordinates.STDistance(h.coordinates)<=(1*1609.344)
order by left(h.postcode,4)

When I am running the above query it is giving lots of postcodes which are not part of that Radius. I am verifying my results with another site http://www.freemaptools.com/find-uk-postcodes-inside-radius.htm and this site is saying that 1 Mile of Radius contains postcode IG1,IG2,IG3, but when I am running the above query my results are coming as E12,IG1,IG2,IG3,IG4,IG5,IG6. Which I am unable to find out why it is giving me this much or post codes in just mile of Radius.

please help