You cannot set up Marketing Cloud Account Engagement yourself to sync with Person Accounts. You need to contact Marketing Cloud Account Engagement support to enable this functionality, as it is not available by default. Person Accounts are a special type of account in Salesforce that combines the attributes of both accounts and contacts. To sync Marketing Cloud Account Engagement with Person Accounts, you need to follow some additional steps, such as enabling Person Account Syncing, creating Person Accounts instead of Leads, and adding Marketing Cloud Account Engagement data to Person Account layouts12 Reference: 1: Person Account Syncing with Salesforce2: What To Know Before Using Person Accounts in Marketing Cloud Account Engagement & Salesforce

Visitors are anonymous web browsers who have interacted with your online marketing content, such as your website, landing pages, or custom redirects. Visitors are converted to prospects when they fill out a form or form handler, which captures their email address and other information. Filling out a form or form handler is the only way to convert a visitor to a prospect. Running through completion actions, matching an automation rule, or visiting a Marketing Cloud Account Engagement landing page do not convert visitors to prospects, unless they also fill out a form or form handler on those pages. Reference: Visitors and Prospects, Forms and Form Handlers

The two steps that you must do in Salesforce to map a Marketing Cloud Account Engagement prospect custom field to a Salesforce field are:
Add a new custom contact field in Salesforce. A custom contact field is a field that you can create and add to the contact object in Salesforce, which stores the information and activities of an individual person who is associated with an account. You can use custom contact fields to store data that is specific to your business needs, such as industry, product interest, or satisfaction score. You can map a Marketing Cloud Account Engagement prospect custom field to a Salesforce custom contact field, so that the data is synced between Marketing Cloud Account Engagement and Salesforce. To add a new custom contact field in Salesforce, you need to go to Setup > Object Manager > Contact > Fields & Relationships > New, and follow the steps to create the field.
Add a new custom lead field in Salesforce. A custom lead field is a field that you can create and add to the lead object in Salesforce, which stores the information and activities of a potential customer who is not yet qualified. You can use custom lead fields to store data that is specific to your business needs, such as lead source, lead score, or lead status. You can map a Marketing Cloud Account Engagement prospect custom field to a Salesforce custom lead field, so that the data is synced between Marketing Cloud Account Engagement and Salesforce. To add a new custom lead field in Salesforce, you need to go to Setup > Object Manager > Lead > Fields & Relationships > New, and follow the steps to create the field.

Explanation
The Marketing Cloud Account Engagement prospect audit capabilities can list all the data that was obtained by Marketing Cloud Account Engagement and how the data changes as the prospect interact with your emails, website, and CRM sync. This is true because the prospect audit table displays details about changes to the prospect record, such as field changes, list changes, assignments, form errors, email opens, link clicks, page views, CRM syncs and more.

Explanation
The correct sequence of events is E C B A D. Visitors access your company website (E), a cookie is applied, a visitor submits a conversion form (B), the visitor is now a prospect (A), and the prospect's activity history is available to view in Marketing Cloud Account Engagement (D)4. This is how Marketing Cloud Account Engagement tracks and captures visitor and prospect data and behavior