OPM GL Expense Allocation on basis GL balances

Hi,

While doing GL Expense allocation, first of all we define allocation code and then attach range of accounts to allocation code.

Now When we define expense allocation basis on GL balances, we enter item code, org code, then we need to enter account as well. Why we need to enter account while we have already listed all accounts range under allocation code? How can i enter more than one account in single row of item?  when is fixed%, account code is disabled. Same behaviour should be with GL balances.

Please advise.

Second question is:-

When we run opm cost allocation process program, there is last parameter in the program, Refresh Instance as Yes or No. I understand that if i say Yes, it will delete  old history of allocation.