In my Citi account shutdown i suspect , multiple payments from 5 diff checking accounts is the reason . The WMBP payments were posting to my accounts quickly, whereas checking account payments were put on hold for 10 days, before the credit limit is increased . When called , they told checking account payment was considered more risker to the comp algorithm then the electronic payments from wmbp, since it was coming from diff banks.

So my theory would be , if you follow 1 single pattern of payment(checking or WMBP) , you should be good. If you mix it , irrespective of volume the computer flags it.

Also continuous purchase of similar larger amounts also are red flags, gc.com/simon.