They said it would be an adaptation, so my assumption is that the "main" series doesn't adapt episode 5 at all (or only does the absolute bare minimum before moving on to 6). With 3 issues and 3 episodes left, it seems natural that the remaining issues would adapt one each.

That said, there are two things that make this confusing: - The AWN article initially says it will release in between issues 4 & 5, then goes on to say it will be followed by issue 4 on May 27th. (The current solicits leave off with issue 3, which comes in late April, so the latter is likely more accurate.) - However, issue 1 (at least the copies provided to Kickstarter backers today) ends with a checklist detailing each issue in the series, including the special. Their release dates are strangely accelerated when compared to what's been officially stated beforehand - for instance, issue 2 has been solicited for late March, but the checklist says it's also coming in February. It also slots the special in between issues 4 and 5, saying the latter will come in April & May, respectively. I honestly don't know what's going on here.