If the default position based attribution model provided by Google Analytics isn't what you need for your Google Analtyics activity columns, you can use the Google Analytics Model Comparison Tool to create your own custom position-based attribution models. Note that Google Analytics supports several different types of models, but Search Ads 360 supports only custom position-based attribution models.
In addition, the position-based model you create can only customize the amount of conversion credit distributed to first interation, middle interaction, and last interaction.
Search Ads 360 does not support models that customize the lookback window, impression credit, user engagement, or that specify other custom credit rules.