P11d quick query

Dear All,  I'd like your view on the following....

Directors loan account, starts year in credit -2k as at 05/04/09.  A series of withdrawals is made against the account so I have treated them as a single loan, the value of which steadily increases during the year to an overdrawn balance of +£6 in mid Nov.  The closing balance is +£15k by 05/04/10.

My question...do I calculate the cash equivalent starting as at +6k in mid Nov, and calculate the benefit over 5months? Pior to this the loan account balance was either in credit or steadily rising below the £5000 limit.

Sorry if its a daft question, but it looks odd when I'm coimpleting the P11d