It would be great if you would put a little badge somewhere on people's profile to let you know if the person you want to attack/hack/raid is within your 40% threshold. I would say the best place to put it would be to attach it to their name so it shows up on enemy shares, the battle page and on their ship page.

Example of all three places:

people on your battle tab are always within the threshold. just kill people off that and you should be fine.