See the appendix to L.A. County Probate rules for guidance. http://www.lasuperiorcourt.org/courtrules/Chapter10-5.htm#10.CA2

See specifically the following rule regarding how a judge determines extraordinary compensation --

9.1.1 Propriety of allowance - "just and reasonable" considerations. The court has broad discretion in determining whether and what amount of extraordinary compensation should be allowed. Generally, the court takes into account the value of the estate, the nature and difficulty of the tasks performed and the time spent, the results achieved and whether those results benefitted the estate as a whole (rather than simply furthering the interests of a particular distributee). The court will also evaluate these factors against the amount of statutory (ordinary) compensation payable, and the extent to which the amount of statutory compensation itself provides reasonable compensation.

Estate of Fulton, 23 CA2d 563, 73 P2d 664 (1937)

Estate of Harvey, 103 CA2d 192, 229 P2d 68 (1951)

See Rule 10.142.