Rapid Fire vs. Close Stationary Targets or RFvCST is a Basic Set: Campaigns pg 408 rule for Rapid Fire under Special Rules for Rapid Fire
"Close" appears to mean "a Size Modifier high enough to completely counteract the range penalty" so the bigger something is, the further away it can be and still qualify as close.
Half (rounded up) hit by default, or ALL if the roll succeeds by the recoil penalty or more.
Very Rapid Fire on the other hand, all shots hit on ANY success against close stationary targets, recoil is irrelevant.