Lets say that A is an important node, lets also say that it has a slightly above average trust weight. It has many connections incoming to it, and many outgoing from it that it makes of its own. Assume that is also has a list of preferred outgoing connections to nodes it knows are of similar importance to it. If you can isolate it then it improves your chances of success slightly.
How do you isolate it so that it can not receive or relay information to anyone without being physically near it?
I assume A is not going to connect to infinite nodes.
Thus I assume there are certain finite number of nodes it connected to such that if they were all adversarial then node A would never know it was occasionally receiving a delayed transaction propagation. Even if there were a few connections to A that were not the attacker, those connections connect to other connections and the attacker may be able to map out the network and determine where to place its effort so that as a mesh it becomes blocked off. If you can't visualize this, then I don't know what to say. I can visualize that in my mind. I don't feel like diagramming it. I don't know how successful it would be. Attacker might just maximize number of nodes by diluting trust and how random luck plays out in terms of the amount of trust cordoned off.
Now as for the probabilities and what would be the ratio between T and 51% - T, I don't know. Would have to develop a formal model and analyze.
Btw the more trust A has, the most incentive to focus all adversarial nodes, on isolating that node.
Note there was a research article I saw recently on how surprisingly hierarchical the Bitcoin P2P network is and how propagation is controlled by fewer super nodes.