It's all about targets with cashback bonuses. The logical conclusion of what you are saying ie lose often - is to set a higher win target. You need a high win target with a very low HA game to maximise EV. The higher the win target the more you will lose and the more EV you will earn. But the trouble is unlike an SNR there is no Betfair for the losing money to fall into! But theoretically you are correct in thinking this way - not hoping to lose but setting a high win target.
IMO cashbacks are dangerous. Take the 20% to £100 type. It's quite easy to lose seven on the spin just trying for a double up. You really need a big bankroll to go for the full amount. Well worth going for a smaller amound of cashback and keeping in sensible parameters.