These Band definitions are system defined and it seems even staff also not aware of the exact rules.. obviously high balances are one criteria..
I would suggest the following to increase the chances of breaking into to higher bands.
try to maintain high balances in deposit products, have some loan products as well and use as many as HDFC suite of products like below:
1) maintain SB balance as high as possible
2)Have FDs
3) Open an RD( small)
4) Open a gold loan ( small)
5) Open an OD on FD
6) start transacting heavily using Payzapp
7) Have a NCEMI on both DC as well as CC
8) Use HDFC bill pay to pay for other banks CCs and any other bills
9) make one or two Bills as smart pay
10) use DC or CC for International transactions attest once or twice
Etc etc
I have done all the above and beyond..
good luck