I've had the 396T for several years and I've been very pleased with the Close Call feature. I don't use the stock antenna that came with it and usually have either a Diamond RH77CA or a RHF40 hooked up to it, which probably helps.
I used to live in downtown Cleveland, and right when every football, baseball, or basketball season would start up I'd sit outside the stadium and log all of the hits, and then use that list of frequencies to listen to all season long. At the Quicken Loans Arena, I was surprised the first time I did this because I started getting hits a good 3-4 blocks away. I think they had all of their radios at max power. I even got a close call hit from a blimp that was flying over the stadium to get aerial shots for the TV. When that happened, I knew that the close call feature & I were going to be lifelong friends.
At the baseball and football stadiums I'd have to be a little closer to get the hits, despite them being open-air stadiums-here again, I think it was due to the power settings on the radios being used. At any location, once I was close (and still outside the stadium), I'd hear just about everything-security, parking, maintenance & laundry crews in the lower levels, etc. At air shows I'd get hits anywhere on the tarmac, and when the city hosted a formula 1 race a few years back I stood outside the gates and close call got each of the race crews & drivers, the TV camera men, and all of the hospitality operations within an hour or so. I'd say everything was a good 500 feet away, if not more.
I recently added an FM notch filter to lower the RF floor. Uniden has a broadcast screen for the FM band that causes it to ignore FM hits, but I didn't know if "ignore" just meant it doesn't sound the alert but still measures the signals, or if it blocks out the FM signals completely. But after adding the notch filter, I noticed it was pulling in much weaker signals with close call, presumably, ones that would have otherwise been missed because I was in the same places before without the notch filter and CC never picked the new frequencies up. It should be noted, I wasn't using the Diamond antennas with the notch filter due to the added length on the notch filter. The Diamond antennas are tall enough as it is.
Some people have had good luck using pre-amps, but I haven't tried that angle yet. But you'll definitely want to use CC when you're mobile, it isn't going to catch as much at home.