You are wrong. The marriage rate between "tigrigna" and tigray people is higher than you think. As a matter of fact, there are lots of "Tigrigna" leaders married to Tigrians and there are many Tigray leaders married to "Tigrignas."
You say you noticed differences and you are not lying. But I have to tell you it's very amplified and exaggerated. To begin with, there is no such thing called "tigrigna" ethnic group. It's an invention by PFDJ/ HIGDEF. If you want to prove this to yourself, google and see the first time the term "tigrigna" ethnic group [not tigrigna language] was ever used. It doesn't go past 2 decades. This is just the creation of the political environment of the recent decades which are characterised by intense competition between the two faak ups led by zenawi and aforqi. Other than that, there is no much historical or cultural difference.
If language is a factor for ethnicity, Ofcourse an american who lives in Buffallo New york speaks similar to A canadian across the border than an american who lives in Texas. Your logic is busted here
I see what you trying to do here but I give you another example. Adigrat is closer to Asmara than Axum and Adwa is to Asmara but Adigrat tigrigna accent is the odd one out despite its proximity to Asmara.