How about this...
There are basically three ways to spend influence:
Planned Influence - This is influence used directly on actions in your DO. Multiple regents can spend influence on an action in the DO (supporters put theirs under "free actions") and it is subject to diminishing returns. All the planned influence that is spent is pooled together and then used to increase the DAC.
Defensive Pool - This is used to counteract other's actions. Actions that other initiate within your sphere of influence (ie. where you can spend influence). Each point of influence (GB or RP) used from defensive pool adds 1 to the DDC.
Offensive Pool - Offensive pool is used to counteract defensive pools. If someone spends influence from a defensive pool to hinder an action you initiated, or to hinder an action that you specified in your DO (offensive pool notes) that you want to assist, then you can use you offensive pool. You can only spend as much from your offensive pool as there has been spent from one or more defensive pools to hinder the action.
Examples & Permutations:
Regent A takes an action within Regent B's sphere of influence. In his DO he spends 15 planned influence to give himself +10 to the DAC. His action activates regent B's Defensive Pool, Regent B spends 10 Influence to raise the DDC by 10. In response Regent A spends 10 Influence from his Offensive Pool to aid the action, giving +10 DAC. The final DDC is increased by 10, the DAC is increased by +20 in total from influence.
Regent A undertakes and action in Regent B, C and D's sphere of influence. Regent A and C spends 30 planned influence to aid the action, giving +15 to the DAC. In response Regent B spends 20 influence from his defensive pool to hinder the action. Regent A, C and D then spend 20 influence from their Offensive pool to aid the action. The Final DDC is increased by +20, the final DAC is increased by +35, through influence.
Savvy?