Mistwell said:
I like it also. If I miss my target because someone was standing in my view of the target, there SHOULD be a chance of hitting that someone standing in the way!
The concept is fine. The implementation is bad because it doesn't work in the simple D&D combat system of generic AC. AC is not 'stacked' from bottom to top with natural armor, armor, shield, dex, etc.
And, as it is, the rule has some odd situations (that admittedly would be very rare). Here's an example, with names to make it easier to explain. An archer (with precise shot and no other relevant feats) shoots an arrow at an orc, standing behind a fighter (ally to the archer). The archer has a +5 attack bonus. The orc has AC 24 (+10 full plate +2, +4 heavy shield +2). The fighter has AC 25 (+10 full plate +2, +4 heavy shield +2, +1 dex).
Ignoring a natural 20 (because that is a hit, and only a hit), the archer normally needs a 19 to hit. If he rolls a 19, he misses, however due to the +4 cover bonus. So, now, does a 24 hit the fighter? No, it misses due to Dex and thus the fighter doesn't provide cover after all*. So, the 19 hits. Now, change the fighter's Dex bonus to +0 and give him a ring of protection +1 (or insight ioun stone +1). Same AC, but now the 19 no longer hits. It still doesn't hit the fighter.
There might be other situations which make things weird, but this was enough for me to discard the variant. The fighter in this example will never provide cover for the orc, but the fighter would never be hit (as cover) and would always provide cover for the orc with 5 more points in AC. That's inexplicable.
* Wait a minute, no cover? What happens when a burst (non-spread), Reflex-offering effect occurs on the other side of the fighter from the orc? Does the orc get a bonus to his save or not?