Most customers touch several things before they buy. A model is the rule for dividing the credit, and changing it changes who gets it, not how many there were.
- Last paid click gives everything to the final paid touch. The default, and the one that agrees most closely with what ad platforms report.
- First click credits what started it, which flatters discovery.
- Linear splits evenly across every touch.
- Position based weights the first and last touches most heavily.
- Time decay favours the touches nearest the outcome.
The lookback window
Touches older than the window are not considered. Ninety days is the default because considered purchases take that long; a shorter window quietly credits the last thing somebody saw rather than the thing that persuaded them.
The count of customers never changes with the model. Only the split does. If a total moves when you switch models, that is a fault worth reporting rather than a finding.