A look at Wikipedia confirms my suspicion that when Ashkenazim and Sephardim read the same haftarah, the Ashkenazim generally start earlier and/or finish later than that of Sephardim. Is there a specific reason why this is so?
The Shulchan Aruch in סימן רפד - דיני הפטרה וברכותיה says that the Haftarah should be at least 21 verses long, unless the theme ends beforehand.
א מַפְטִירִין בַּנָּבִיא מֵעִנְיָנָהּ שֶׁל פָּרָשָׁה. וְאֵין פּוֹחֲתִין מִכ'' א פְּסוּקִים, אֶלָּא אִם כֵּן סָלִיק עִנְיָנָא בְּבָצִיר מֵהָכֵי
It would seem that different congregations had different ideas as to what belongs to the main theme of the Haftara.
A quick perusal of your link shows that Sephardim have many Haftarot with fewer than 21 verses, and Ashkenazim have almost none of those.
It appears that Sefardim had a narrower definition of what can be included in a theme.
It's now left to somebody with spare time to analyze each case and explain how each congregation themed each Haftarah.