4. An additional fee may be negotiated between a sheriff officer and the instructing agent by prior agreement in the following circumstances–
(a)where the sheriff officer is standing by awaiting the delivery or uplifting of a document for immediate service;
(a)where the sheriff officer has to instruct an huissier or other officer of court outwith Scotland to serve a document; or
(c)where there is no prescribed fee and the importance, urgency and value of the work involved necessitates an additional fee.