This may be slightly off-topic (although it's still semi-related), but I've been doing some thinking on this topic lately and... Is there really even that much of a historical justification for a tall empire being capable of truly succeeding as a long-term thing? Why are people so obsessed with this idea across strategy games in general? It seems like a "tall" empire wouldn't even be an empire at all. I think of "Tall" as being more of a transitional state between fully exploiting Sol and conquering the galaxy more than I do as something I'd want to continue indefinitely.
Even if you fix science so that research rates are independent of empire size, the bigger empire should still be at an advantage even with the implementation of tech spread.
Aside from some geopolitical factors (e.g a coalition attacking the large empire on several fronts) and geographical factors (e.g tall empire has nothing but bottleneck systems bordering you), I don't see a scenario in which the sprawl empire doesn't roll over the tall one every single time or at least win the long game. People seem to have this fantasy where that's not the case, or that it shouldn't be "in the name of realism".
This is not how things actually work in reality, if it did then Earth would be governed by one super power by now. No... nothing is really binary and games such as Aurora do not model most of the things that impact any nations ability to influence another. Those you have to do with RP in this game.
The condition you ascribe to any power only exist in games. In real life no one would aspire to be either tall or wide, that would be a state one would be in for some reason or another in comparison with something else.
You sometimes need abstract mechanics to sort of simulate the more dynamic and complex part of life that is difficult to represent in details in a game. Things like politics, philosophies, social factors and the like. There always is a balance between what is fun and what is realistic. In most cases this is due to games allowing the player to simply control too many things and allowing the player to be too many functions at the same time that would otherwise not be able to cooperate as efficiently in reality, thus producing rather binary results that are not even remotely realistic.
Aurora is no exemption from this but the difference between Aurora and most other games is that it is a framework for RP which is why it allow you that freedom to decide when you want to restrict certain part of the game or introduce real life politics, unrest or even revolutions into your games.
This does not mean we can improve om some of the basic ideas such as a changing research or economy to make them less binary by nature but still retain allot of freedom.