Roger Norris]So why do Spiders take so much flak for being impossible to hit? I would argue that there's not a Spider-specific hit registration problem, on but that the narrow side profile and high speed make it a particularly obnoxious target. Weapon convergence issues exacerbate those problems even more. And if I, said:
First, let's do a simple size comparison. When viewed from the side, a Jenner is 2.3 times wider than a Spider. So that's already a point in favor of the Spider. Incidentally that's also why Locusts die so easily; they are relatively wide, and target width has more impact on survivability than height (or speed IMO).
Next, consider weapon convergence vs. a moving target. Let's assume that you're in a Yen-Lo-Wang and you want to give the enemy a taste of your AC/20. He's a speedy Jenner whizzing past you at 130 kph and at a distance of 50 meters. Based on the AC/20 projectile speed you need to lead your target by 2.01 meters. Fortunately the Jenner is almost five meters wide, so you can just aim at the tip of his nose and score a direct hit. Weapon convergence isn't a concern at all because your crosshair is on the target (i.e. perfect convergence distance).
But what happens if that target is a Spider? Weapon convergence is an issue because our lead distance is now larger than half the target's width. Our crosshair will not be on the target... which means that the convergence distance will vary depending on the terrain behind the target! In other words, you must vary your lead distance depending on what's behind him. To make matters worse, our AC/20 is roughly 3 meters to the right of the cockpit (more than the width of the Spider FYI), so lead distance varies even more depending on whether he's running clockwise or counter-clockwise.
Well if you crunch the numbers then it turns out you must lead the target somewhere between 5.2 meters and -1.2 meters. That's right - if the Spider is running clockwise (left-to-right) and the terrain behind him is distant then you actually have to aim behind him. But that's very close to his actual width, and if you mess up and put your crosshair on the trailing end of the target? Suddenly the "correct" convergence distance causes you to miss entirely.
That last bit is more troublesome than you might think. It turns out that in some circumstances it's actually impossible to hit him.
Consider a Spider running at 130 kph at a distance of 50 meters. But in this example there's a hill behind him at 100 meters. Taking weapon convergence into account (we're still in a Yen-Lo), we can calculate two different lead distances depending on whether our crosshair will ultimately be on the target or off the target (i.e. correct or incorrect convergence distance).
With correct convergence distance we must lead by 2.01 meters.
With incorrect convergence distance (i.e. crosshair on the hill behind him) we must lead by 0.41 meters.
Notice the problem yet? Half of the Spider's width is about 1.08 meters... it's impossible to get the correct convergence distance to score a hit! If the crosshair is directly on the target then we'll always miss to the left of the target. But if we lead to the right then our convergence distance changes and we always miss to the right!
Moral of the story? I don't know, bring some streaks? Or aim for the foot - convergence distance is less of a problem when the ground is right there.
As a quick follow-up, I would just add that it's a slight exaggeration for me to say that he's totally impossible to hit in that last scenario. You can usually force a fixed convergence distance by leading an extremely narrow point on the target - his hips, for example. But it'll very tricky to score a hit when aiming at the narrowest part of an already narrow 'Mech, and it'll require a lot of game sense to compensate for the terrain behind him. Better just bring some streaks
It explains a lot if true.