I agree rewards are not transparent enough and they have a bit of randomness to them that I don't like. That being said they always grow for me as I get in better and better levels, with some exceptions along the way.
I was also quite sure they depend on amount wagered, not on won or lost tickets.
I got 4500 XRP on diamond levels when I have lost huge amounts while on the next level I literally got 18 XRP because I was winning so it only depends on your recent luck, the more you lose the more you get which makes sense but never feels good if you are winning.
4.5k xrp is a lot of money but you said you also lose huge amounts? How much would that be? Is the amount you lose higher than the bonus that you get? But you still must be thankful because at least you recovered some of those money even if not all but it's strange that you only got 18xrp on your next level.
Normally on other casinos you can claim more rewards the higher the level or rank you reached and it does not matter if you lose or won, but how big is the money that you win anyway? For some that wins huge maybe they won't really mind other forms of bonuses but there are some big players which also care for the bonus.