Protech is correct. A 10db value pad should suffice, just be sure to add that value to your test point compensation in your meter. Also, the lack of port terminators on a tap should not cause standing wave, however they should always be used to prevent ingress/egress and theft of services. I would instead look for Housing terminators (on eols) that are bad or don't have their seizure screw tightend.
Unless the QR 540 connector looks fairly old, you cannot tell by looking at it to determine if its the new type or not. You have to pull the connector apart and look for the radiation shield, the old type connectors will be made of metal and the new will be made of plastic (usually tan or black in color), this is on the pin fitting and not the center or back nut.
This is CABL.com posting #246838. Tiny Link: cabl.co/mbcnq