I keep it simple. I never pick a camshaft based on how I think it will idle. I pick camshafts based on how I believe they will run, given a particular combination and let the rest fall where it may.
Most of the time that's beating a dead horse though. I can't TELL you how many times someone has said to me "Oh but I want the idle to sound like..." and pick your car. His dad's 66 whatever. His buddies 72 whoknows. The local street guys 69 thingamajig.
Hell, it's such a thing comp came up with it's own line of cam's just to target that idea. Nevermind those cams are out of wack. 235/249 duration at .050? With .497/.483 lift? Stupid.
People need to realize that when you build a strong motor. With planned out and matching parts. Then you get rewarded with that oh so sweet cracking rumble we love to call idle.
As for LSA? I always thought of it as working more in conjunction with duration to affect idle. Obviously a tighter LSA on the same duration increases overlap. And more duration on the same LSA also increases overlap. As for how much each affects it on it's own? Of that I am unsure.
Would be interesting to grind a cam. Vary the duration/lsa. And then run them all and see what you end up getting.
As for the race head's on a 318. It makes sense to me compression would stay the same. No matter how fast you fill a glass, it can still only be filled so much right? Same as a cylinder. If my analogy makes sense.