When I was playing there, I maintained a circa $25 average for about 2 hours. I'm an international player, and was staying elsewhere, so they were aware this was "ex-gratia" play. That said, I spoke to a host, who gave me an OPEN coffee shop comp, on which I managed to spend $130 with a friend. Great return. 2 hours X $25 per hand x 60 hands per hour = $3000 playthrough, with expected house edge of about $30, and got $130 comp.
I can't speak of whether everyone's experience would be the same, but that's what worked for me.
So, for clarity, my belief is you can be rated for ANY amount at those tables, as long as you have a player tracking card. The higher your bet the better your comps should be - but in tight times, casinos are often appreciative of any play, so don't feel you have to bet black to get anything of value.