Horse racing draw advantage bias
Both the Rowley course and the July course are sometimes split in half using a temporary running rail.
Races are then run on either the Low half of the course, or the High half of the course.
At present, there is no indication in race returns of this course splitting.
I would guess that in general, results showing Low positioning of the stalls will mainly be run on the Low half of the course, and races with stalls positioned High, will mainly be run on the High half of the course.
Results with stalls Centre could have taken place on either the Low half of the course or the High half of the course.
As described in the Racing Post's "Top Draw" feature, the stalls can be positioned in 6 different places due to course splitting.
High, Low and Centre on the Low half of the course, and High, Low and Centre on the High half of the course.

Horse racing draw advantage bias NEWMARKET JULY 6F
Stalls positioned LOW (L) and Centre (C) 
2 charts
See High positioning on bottom chart

Link to course and distance menu

WINNING STALL NUMBER

 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22
No

of

R

U

N

E

R

S

8   1 C 1     11  1
9 1111       11 1      
10     1     1 11 C1     Stalls positioned LOW
11 1         11   C     1
12 1       1 1   1        
13   1    1   1 1 1     1    
14   11                          
15                 1   1 1        
16       1             1          
17               1         1   1    
18     1   1         1              
19                               1 1    
20 1   1 1         1 1               11    
21                                          
22                                            
6 3 4 1 1 5

<--Good or better -->

3 5 4 6 2 2
18 20

Copyright 2005 [H Hutchinson]. All rights reserved.

A very weak pattern.
At first glance, this looks like a high draw advantage in races of 10 to 17 runners. 
However, on good or better going, in races of 10 to 17 runners, the Top 1/2 of the draw only won 12 of 21 races.
The Bottom 1/2 won  6 of 21 races.  3 races were dead centre.
There is no clustering of results anywhere on this chart.
2006 results :-  3-10,
10-15, 15-17, 1-20

NEWMARKET JULY 6F
Stalls positioned HIGH See chart above for Low and Centre positioning.

WINNING STALL NUMBER

 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22
No

of

R

U

N

E

R

S

8 1     1   111   1
9 1   1 1 1     111 1
10 111   1     1 1 1 11 1 Stalls positioned HIGH
11 1         1     1   1
12 1 1       11   1   1    
13   1    11             11    
14   1                          
15 11        1  1       1 1   1   1
16 1                       1      
17                   1     1        
18                   1                
19                                      
20                                     1  
21                                          
22                                            
8 1 2 2 0 6

<--Good or better -->

3 4 2 8 5 4
15 25

Copyright 2003 [Howard Hutchinson]. All rights reserved.

The Top half / Bottom half split favours the Top half by 25 wins against 15.
On good or better going the Top 6 stalls won 26 of 41 races 63 %.
You may choose to follow that trend, but there are definite spreads of results in races of 9 to 12 runners, and no clustering of results above that.
In 2006, wins were spread.
On good or better going the Top 6 stalls won only 2 of 6.
Stalls 1 to 6 won 4 of 6 races.
As in previous years, there is no recommendation.

2006 results :-  3-9, 1-12, 6-12, 10-12, 1-15, 5-15, 11-15,