The issue is the smaller powers don't want the entirety of Imperial, Federal or Alliance space hitting them as its a fight they just cannot win. Sure they have less they need to fortify but if they need to fortify most of their systems every week to avoid heavy turmoil they're going to run out of cash and morale. Even with favourable triggers the smaller powers will struggle keeping their expansions going if they've got a full scale Fed or Imperial undermining effort ongoing, Mahon has one of the largest and most dedicated cargo pushing playerbases in the game and even they don't get every expansion through when up again Federal undermining, nevermind a small little RP power like Archon or Antal
You can't be a pacifist and expand endlessly while also avoiding conflict. It's just impossible in PP.
Additionally, you still consider the power to be functioning alone, as if the Federals will oppose the expansion no matter what. I said that the power should be taking advantage of opportunity, not going smashing against the wall.
Let's take for example the current situation, where the Feds are against the Alliance and the Imperials together. Both the Imperials and Mahon do offensive expansions against Hudson/Winters. If Hudson has 2 expansions on their space from Mahon, 2 from ALD and 1 from Patreus, they got their hands full and they have to focus on it. This means that if Antal, Delaine or Sirius try to get a system that contests 1-2 systems, it is a lesser evil and will be ignored, because they have bigger fish to fry.
Same goes if Winters and Hudson has offensive expansions on Mahon. Once again, a matter of opportunity. That's the whole point, to act when they CAN'T throw their entirety on you.
Patreus is a also a fairly small power in terms of supporters and they have indeed managed to get an offensive expansion in just a couple weeks ago. So there's your example that what I'm saying is indeed possible. And that wasn't even a sneak attempt of 1-2 systems contested.