euroson1,
The reason for the add on is the difference between the two game scales. ICON usd a 1-5 scale with 2 average, where as CODA uses 2d6 with a mathematical average of 7 (although the method of attribute generation tends to push the CODA stats up a little).
If you don't like the 2xICON ATTRIBUTE +ICON EDGE+2 you can try something different. It just any conversion isn't going to be perfect. For instance:
ICON STAT+EDGE CODA STAT
-1 2
0 3
1 4
2 7
3 8
4 9
5 10
6 11
7 12
(8) 13
The mathematical difficultues rise from the fact that 2 is average in ICON rather than 3, resulting in a "bowed" curve. For instance a human's Strength score in ICON can range from an effective score of -1 to +7 with 2 as average. In CODA it is a 2-12 range with 7 average. For a mathematical conversion you'd have to compress values below 2 and expand values above 2.
But for a game you'd probably want to switch the values a bit so as to spread out the attrubite bonuses.
That's the thing about conversions. You can't reall match up abilities exactly in two different systems. That why the GM and players need to focus on try to maintain the spirit of the character, and fudge the conversion to fit.