Make consistent. Use relative boni only. Raise the champions superiority 3.75 times stronger than a base unit.

e.g.
An advanced experienced entity is:
    advanced_stats = base_stats * advanced_modifier
=>  advanced_stats = base_stats * 1.25 => 1.25 as strong as a base unit.

A veteran unit currently is:
    veteran_stats = base_stats * advanced_modifier * veteran_modifier
=>  veteran_stats = base_stats * 1.25 * 1.5
<=> veteran_stats / base_stats = 1.25 * 1.5 = 1.875 as strong as a base unit.

    champion_stats = base_stats * advanced_modifier * veteran_modifier *
champion_modifier
=>  champion_stats = base_stats * 1.25 * 1.5 * 2
<=> champion_stats / base_stats = 1.25 * 1.5 * 2 = 3.75 as strong as a base unit.