@elli_wodify: You hero! This is a great workaround for me, thanks for reporting back! 
It does seem to be a bug with the splashscreen plugin:
https://issues.apache.org/jira/browse/CB-9240
Off the back of that discussion, I am now using this forked plugin instead of the official cordova plugin until they fix the issue. The forked version comments out a whole block of code in the load method but it seems to be interconnected to your solution.
I still think there may be an issue with iPhone (especially iPhone 6 plus) in landscape mode, even with this workaround, but I need to fully device test before coming to any conclusions.
Anyway, thanks again!