Hi Kamk,
For "performance" I mean: damage, accuracy, speed...
I wrote 15 to 20 meters, but is just one example ... could be 4-6 meters. The goal is to discourage the blob tactic.
When you have 5 squads and retreats two squads (for example) the "damage, accuracy, speed..." of single squad improves... from 41% to 64%, see the image below (green line). The cost under the green line suggests that the cost of a Blob 5 units (for example) is 1250 MP, but is efficient as units that cost 512 MP ... and this is not convenient.
I think that in this way no one would blob larger than 2/3 squads ...
http://www.coh2.org/file/10396/coh2-blob.JPG
Personally i would highly benefit from it, and i also always loved the idea, but...
...it might severely hurt factions with forward HQs, or anyone who has to do a retreat of several squads. It would become nearly impossible to defend any kind of reinforcement point properly.
Or just imagine bottlenecks, which would become unbreakable - might indirectly buff usage of barbwire though.
My point being: rather thin line between either useless, or too strong. Your suggested 20% for "everything" is way too strong IMHO. I'd go in the more slight debuff direction, like... 10% more incoming accuracy per squad nearby in 5 meter radius, or a few percent less accuracy - stuff like that.
Edit: just to prevent misunderstandings: i like your idea, just trying to throw in some food for thought.
@Jespe: if you ATnade / Faust a tank you still need your AT to finish the job. Do the same with MGs, and keep high dps squads nearby.