What is the test for presumptive effect on allocation in an indemnity action?

"... We find ... no justification for giving presumptive effect to an allocation that is not the product of adverse negotiation. A presumption that the parties have reasonably allocated a settlement amount between issues in the action should be reserved for a settlement by parties with truly adverse interests in the allocation. [Citation.] Where the parties have purported to settle an imaginary dispute over allocation, that allocation should be given no special treatment in an indemnity action. Plaintiff should be required to prove the reasonableness of its proposed allocation by ordinary means." (Ibid.; see also Gouvis Engineering v. Superior Court (1995) 37 Cal.App.4th 642, 650-651, 43 Cal.Rptr.2d 785.) ¹⁰