My understanding is that many who've tried cutting the orange into less or more than eighths has either ended up with too little or too much pithyness. Might be a totally fine mod for someone who's done the recipe and knows what they want, but I'd think that for someone new to the recipe 8ths is actually a fairly important part of it.
Agreed, reading through the entire JAO thread Joe himself states that he found the recipe worked best (to his tastes) when cut into 8th's, though many people find no issues with smaller pieces, and some go to great lengths to reduce pith taste via peeling etc.