I've been thinking, if you can't get that Lightweight Frame on your Unguided Rockets/Punisher because you need those 2 points elsewhere, I'd say it's still worthwhile to take Long Range Scanners, that way you can acquire the target lock early on when there's a distance (and later on, although with lower PS it's more difficult to judge) and then if you do get an enemy at R1, go for the primary since then you can use the Target Lock and Focus.
When you're anywhere near range 3 you're going to want to focus anyway in all likelihood.