Maria's percentage of bank betting IS a flat stake betting method [a flat stake % of bank].

'Progressive betting' is a different animal, one that increases the bet stake after a loss with various degrees of increase etc. which range from very mild to very aggressive.
It's still a loss chasing system and all promoters of them [regardless what the progressive method involves] NEVER call them a 'loss chasing'. Why? Because chasing loses is a well known big punting no no. However, that's exactly what all Progressive staking methods are .... loss chasing systems.