To shave the percentages that close, it's important to identify the races that will used to determine voting strength. As I understand the initiative, if approved, it would be active in 2007. That means that the 2006 statewide election would be included.
The commission is required to provide county, township, and voting precinct population values to persons interested in submitting plans. I don't know if there is a geographic component implied, but it would be reasonable to include a simple application, that would permit clicking on an area and have vote totals accumulated. This would facilitate generation of submitted plans in a format that the commission staff could aggregate and provide to the public.
A different set of elections would change the plan, and perhaps the highest score possible, but I am confident that the maximum score would result when districts are taken right to the breakpoints of 0%, 5%, and 15%.
The measure calls for three closest non-judicial federal or state statewide elections (including the presidential race). Judicial candidates are nominated by parties, but don't appear under the party labels. Federal elections would include senatorial races (the last two weren't close). Races would include those in which the two major party candidates received 90% of the vote, but the partisan index would be based on the candidate share of the two-party vote (which is the figure you have used above for the presidential races).
How the 3 closest races would be determined is ambigiuous. It could be interpreted as measuring the margin based on percentage or on based on absolute vote totals. Selecting the elections on the basis of percentage is consistent with how the partisan index is derived. But a more literal interpretation would base it on the absolute vote totals, which could result in down-ballot state races being used because of lower turnout. The 90% criteria could also come into play. If 3rd party candidates receive almost 10% of the vote, the percentage margin to the 2-party vote will be widened slightly over the percentage margin of all candidates votes.
Text of relevant section of proposal:
Section 4. (E) The “three closest general elections” means the three general elections for non-judicial statewide federal or state office, including the offices of president and vice president of the United States, held in any of the four previous even-numbered years immediately preceding the year in which the independent redistricting commission must adopt a redistricting plan under this Article, in which the statewide margin of victory between the partisan candidates with the highest and second-highest vote totals was the narrowest and in which such candidates received combined votes equal to at least ninety percent of the votes cast for all candidates for the office.
