Limited Power of Attorney

Hi everyone. A question about limited power of attorney; does anyone one know generally or had experience specifically about how states interperate a situation  where the document specified that the Advisor was only allowed to make withdrawls of pre-agreed fees from the account? I've read that if you're allowed to make withdrawls this can be interpreted as having custody and that can cause major headaches which I don't want. However, the ability to make withdrawls of fees does seem much more convenient than having to make the client cut a check each quarter to pay the firm. 

Thanks in advance for your perspective.