As far as I know, most European airlines use identical seats in business class on short-haul. There are no competitive reasons for Finnair to do otherwise. Indeed, contrary to your belief, Finnair and NorRA definitely do move the class divider according to demand.

The middle seat is blocked on A320 series. There are no middle seats on E190, so you just have to hope that business class is empty.

Generally speaking, there is exactly one thing that is impressive about the Finnair short-haul business class: the list prices. Impressively high prices, that is. I believe every regular here agrees that short-haul business class is only meant for long-haul transfer customers and for upgraders.