Tryptamine may be added to a degree far beyond the limits of the enzymes naturally present to process them without any negative effects. One gram of tryptamine per quart jar of spawn produces fruits with potency of 3x to 4x that of the untreated jars.
A person attempting to make a novel tryptamine would want to completely saturated the synthetic pathways with the novel tryptamine precurser to ensure that the target compound was the only one being produced. So adding a gram to a quart jar of spawn, and then casing the spawn directly instead of using a bulk substrate would be most effective to prevent other competing tryptamines from being synthesized and producing a mixture of 4-ho-dmt and the target compound.
To know the exact ratio a person could make say ten jars of spawn with varying amounts of tryptamine and then test the resulting fruits for potency. The first jar to have a drop in potency is obviously near the saturation point which could then be used to determine how much 5-meo-dmt needed to be added to saturate.
Any added compound should be ph 7-8 before being added.
^If you have any links to that information it would be appreciated