These are the factors that went into determining the "smallest warship my empire is likely to field"
First, I wanted efficient engines, size 50s. That way, I could have the largest range possible for a given amount of boost, or the smallest ratio of fuel tanks to teeth.
Second, I needed enough engineering spaces so that I could fix the largest system at least once, generally more than once. And for my boosted engine ships, that meant that they would have to have at least 2 size 50 engines.
Third, I used 15,000 ton civilian jump tenders/tankers to support my exploration. So I would have a great deal of flexibility with military ships with civilian engines that were smaller than 15,000 tons. I finally built some 22,500 ton tenders, but bigger is going to have to wait for better jump engine tech, and suddenly everything has a higher priority than that.
So there was a feedback loop, I have the infrastructure to move size 15k and below military ships everywhere in my empire on short notice, to move bigger ships, I would need a new tech and a new infrastructure. But I have built a lot of smaller ships, so I don't have a demand for the new tech and infrastructure. So it keeps getting put off. And so as a result, I am not adopting a fleet strategy that requires the largest possible ships either.