While I truly have no idea, I think that the business plan for Venmo is person to person transactions. All my activity with Venmo is paying or receiving small amounts of money from various other people (small as in <$200).

If you are doing only debit purchases, it may draw rats eyes. On the other hand if you have 15 P-T-P transactions and interspersed with those is a few small debit purchases, I suspect you are good to go. However, I do value Venmo's basic modus operendi for paying friends without having to dig into my wallet so I don't do anything to screw with it.