I think we have to agree that one of the conceits of the universe is that you do have to get very close to gather anything meaningfully. In theory you can just park a satellite somewhere between the Oort cloud and the system proper, even a few light minutes away, and just hoover up all the EM that oozes out over time. But then sigint is basically just 2,000 satellites per House/faction, and their intel gathering is amazing.
We know that capability doesn't exist, so have to accept that along with crap weapon ranges and 'Mechs being king, signint requires true liability in proximity to your intended targets.
I'll offer a thought on this particular point:
Yes you can insert a satellite like that and hoover up all sorts of intel but it has the problem of then that information is not useful until it gets back to your mission planers, which are going to be in a different system 99.999999% of the time.
Since the conceit of the setting is Black Boxes and HPGs are not that common(and for the later are not under your nation's control in most cases) that means that you have some decisions to make on how to make that information actually useful.
The tactic I see here is you jump in somewhere between the local Oort cloud equivelant but still more than 15 AU from any known inhabited bodies/known stations.
Deploy the satellite on a long slow coasting trajectory, maybe a couple others to do line of sight communications around celestial bodies, and have a controller ship sitting say about 30 AU out.
Communications delay will be a few hours by that point but done right no one would even notice it when the intel ship jumped in or out and the satellites could easily go unnoticed for years.