Contribution levels can be based upon employee classes. If the employer can clearly define classes for employees, different amounts can be offered. However, if you have two employees doing the exact same job (i.e. if you have two full-time receptionists) they must be given the same amount. For a PHSP, if the sole proprietor has a full time employee(s), they can only contribute for themselves the least amount they are giving their full-time employees.
Hot tip: If you are a sole proprietor and employ your spouse, rather than opening a Personal Health Services Plan for yourself, you can set up a Health & Welfare Trust for your spouse that has no limit on contributions, and no expiry on deposited funds.