The origin of the idea comes from the typical setup of a D&D adventure.
Mages and casters in general *are* supposed to be weak in melee. They don't just rush into the front line of any battle.
The dumb strong tanks are the ones that protect these weak spell casters from the point end of daggers and swords.
So adventurers head out in groups, main buff tanks cover the front, and caster classes at the back for support.
In cases where you have no real tanks (solo caster or a group of casters), you just don't go to dungeons unless you hire some grunts from the local bar.
Now explaining the idea of spell disruptions.
- Casters are most dangerous (even in dragonlance series) when they manage to get the spells off. However, it is very taxing to their mind and concentration. You just don't cast a spell like you do spitting out a gum when you have darts/arrows/blades coming to your head every single round. You'll be lucky if you don't get the spell wrong and have them targeted back to your own group.
As to what weapons can go hurt what lines. Since we have max of 4 lines (min of 2 lines) in any battle, we have the following definition
0. Short range melee: This is default weapon, and can only hurt adjacent line, ie front line to opposing front line.
1. Pole arms, whips (Long range melee): This can cross 1 line. Ex, back line ppl can reach opposing front line target. Front line can reach opposing back line. Not every classes have pole arm skills. This limits or makes some particular classes more useful. Because of the long reach, it will have -hr on short melee (ie front line vs front line).
2. Bows and crossbows: This can cross 2 lines. Ex, back line archers can aim at opposing back lines. We can still disallow bows for short melee or just put some -hr on adjacent line. So an archer can shoot (without penalty) the enemies both front and back line if they are at the back line. They can only shoot the back line (again without penalty) if they are on the front line.
3. Long range spells (like magic missile, ice storms) can be cast on any target (ie it crosses 2 lines). Chance of disruption kicks in every round if they are hurt by spells/melee/long range.
4. Short range spell can only touch adjacent lines. This include buff spells, or spells like harm/shocking grasp where touching is involved. Can only be used when casters are on the front line.
Changes in "kill" command.
1. Kill "any opposing member": Melee attempts on targets that you cannot reach will result in random targets on the opposing team that you can reach.