@Dogen This site explains a different rule than you cite in your phonetics series for when the second component of a noun compound has 5+ moras, and it seems to have less exceptions (for example it works for 誕生日プレゼント): http://www.coelang.tufs.ac.jp/mt/ja/pmod/practical/02-07-01.php …
Thanks for the resource! Currently don’t have my computer but I believe the guideline I introduced was for compounds that have a total of 5+ mora, rather than 5+ mora in their later element.
