(nealhunt @ Jan. 04 2008,13:15)
QUOTE
Keeping it a flat 15cm-from-attacker leaves other, equally goony exploits in place. A horde army could easily surround a valuable formation, being intimately intermingled with it, yet still have the guarded units more than 15cm from the formation edge, making it impossible to assault except by exceptional circumstances or abilities.
"Oh, look, my Deathstrikes are 16cm away from your forces. Even though their entire screen of 100+ men were just crushed in assault and the DS are threatened with being overrun at any second, they stand their ground and don't even gain a blast marker."
The difference is that the potential "victim" of the exploit can avoid it under the current rule. Under the flat-15, the victim cannot avoid it.
What is to stop a horde army doing this now? You just move your units a bit and there is no intermingling, but still 16cm distance and those Deathstrikes still cannot be assaulted, and the 'exploit' as you call it is still in place with the current rules.
(That means you have to hack your way past a defending formation to get to the units behind it, regardless of how the rule is written. Isn't that the whole point of having a defending formation though?)
The rule as written doesn't help here in the situation you describe that I can see, and causes problems elsewhere.