Proportionately. The investment is weighed against what it costs to buy or establish this particular enterprise, with no universal minimum figure, and marginality is assessed separately.
Relative to this business, then tested again
Hypothetical example: Because the test is proportionate, a modest sum can be substantial for a modest enterprise and a large sum can be insufficient for a costly one. The comparison is documentary: the purchase price or establishment cost on one side, the committed capital on the other, both evidenced. Passing that test does not finish the analysis.
Marginality asks whether the enterprise has the present or near-future capacity to generate more than a minimal living for the investor and family, or will make a significant economic contribution, and that question is answered from the business's own financial records and realistic projections rather than from a template. A Cavan Monaghan buyer should obtain the target's actual books during due diligence with this second test in mind, because the accounts that inform the purchase decision are the same accounts that will be read later.