We do not have historical records about arrival of Serbs to Croatia, except a few but it's from Bosnia.
Genetics does not show migration from eastern Hercegovina, because genetic evidence for that does not exist.
Prove this migration path with genetic data, in Montenegro also exist and Croats so it is possible that they also come to Croatia, however as I speak genetic data for that migration does not exist.
Prove this migration with genetic data, till then you talk fairy tales.
If part of Croatian Serbs have R1a subclades similar to Croatian R1a subclades then it is possible that they are same origin. Otherwise then all Croats with that R1a subclades come with Vlachs which is unlikely because it is an haplotype that comes with Croats in the 7th century or in the time of Slavic migration.
You have genetics and prove it.
This is one of proofs that Vlachs are coming to Croatia, give me historical records about arrival of Serbs to Croatia and especially from Eastern Herzegovina.
Vast majority of Serbs from Croatia came from eastern Herzegovina, Raška, northern and western Montenegro.
There is no Serbs from Croatia which originated from Kosovo and southern Serbia, these are fantasies.
Serbian village in Dalmatia -
Baljci [video]https://en.wikipedia.org/wiki/Baljci[/video]
Village in eastern Herzegovina (near Bileća) -
Baljci [video]https://en.wikipedia.org/wiki/Baljci,_Bileća[/video]
Serbian village in Dalmatia (near Knin) -
Riđane [video]https://sh.wikipedia.org/wiki/Riđane[/video]
Village in western Montenegro (near Nikšić) -
Riđani [video]https://sh.wikipedia.org/wiki/Riđani[/video]
Serbian family
Krivošija from village Plavno near Knin in Dalmatia [video]https://www.poreklo.rs/2012/06/04/poreklo-prezimena-selo-plavno-knin/?script=lat[/video]
Serbian tribe
Krivošija from Old Herzegovina (modern western Montenegro) [video]https://en.wikipedia.org/wiki/Krivošije[/video]
Serbian tribe
Macure migrated in 15th century from nothern Montenegro to Dalmatia (Bukovica)
[video]https://en.wikipedia.org/wiki/Macure[/video]
[video]https://sr.wikipedia.org/sr-el/Ервеник#%D0%9F%D1%80%D0%B5%D0%B7%D0%B8%D0%B C%D0%B5%D0%BD%D0%B0[/video]
Serbian family
Rašković from village Žagrović near Knin [video]https://actacroatica.com/hr/surname/Rašković/[/video]
Raška (Grand Principalityof Serbia) [video]https://en.wikipedia.org/wiki/Grand_Principality_of_Serbia[/video]