Planning Performance Agreements charging methods - Public forum - Planning Advisory Service (PAS)

I would very much like to get a bit of feedback from Planning authorities on the pros & cons of either charging hourly rates for PPAs, or using an upfront standard rate depending on scale of development (e.g. super major, large major or standard major, etc.).  The latter process seems less complex administratively as it does not necessarily involve time recording and the associated gathering of this data from various parties involved.  I would be very grateful for any experiences of either method of charging.  If you employ a charging method that is a hybrid of the two I would like to hear how effectively that works also.  Many thanks. Regards, John