def calculate_similarity_index(ratios_dict: dict) -> float:
    """Returns index representing string similarity from ratios_dict.

    Index drops the lowest 2 string matching values to reduce chance of Type II error, 
    and missing matching strings.  This makes the index more likely to identify potential errors. 
    Note, one of these values is likely from the double metaphone algoirthm, which returns 0
    when the strings are not homophones.

    Args:
        ratios_dict (dict): Dictionary of ratio values.

    Returns:
        float: Represents the Similarity Index between two strings.
    """
    vals = [ v for v in ratios_dict.values() if isinstance(v, (int, float))]
    for _ in range(2):  vals.remove(min(vals))
    return round(sum(vals) / len(vals), 2)