You get four segments per continent in any case (except 6 in NA). The difference in the continent of origin is that you can't buy two more, and stopovers (>24 hours) are limited to two. Other than origin, stopovers aren't limited.

Intercontinental segments don't count against either the departure or arrival continent's limit.

Also be reminded that OWE's are limited to a total of 20 segments now, no matter how many continents you buy.