Why can't I create two rules with the same Determining Factor Set for the same Tax and Rule Type?

I am attempting to create separate rules by state under the Determine Tax Status rule type using the same Determining Factor Set.  I am creating the rules to identify multiple exempt product fiscal classifications (i.e., condition sets) that apply in each state.  After successfully creating the rule for the first state, I get the following error when trying to create a similar rule for the second state: "This determining factor set code is already associated with a tax rule for this tax and rule type."  I am using the "Set as Geography Specific Rule" function to distinguish between states when defining the rule rather than building the geography Determining Factor into each condition set, thereby increasing the number of condition sets I must create.