with Amex MRCC you can get 5.4% reward rate if bills are 20-21k per month as above that reward rate% decreases..
1) Buy 5k * 4 Amazon gift card vouchers via Amex Gyftr where you will get 800 RPs (2x for MRCC card) [1RP for every 50Rs spent]
2) Via point 1, you are completing 4 transactions of 1500+ so 1000 RPs
3) Again via point 1, you are completing 20k per month (needs one time enrollment), you will get 1000 RPs
so overall 2800 RPs per month and 33,600 RPs per year, for 20k per month/2.4L spends you will get 2nd year waiver off as its 1.5L limit only and if you take 18k RPs for 7k Amazon voucher then 1RP ~ 0.39Rs so 2800*.39 = 1092 Rs/20k = 5.4% reward rate