Yes, a placemat can undoubtedly overlap the runners. But you need to make sure that the combination does not look clustered. Today people appreciated the minimalistic approach. And the combination of two vibrant prints or colours along with that much tableware (spoons, forks, plates, bowls, knives, and glasses) will create a noisy feeling on the dining table. Therefore, if you want to use both runner and placemats, make sure the combination is not compromising the contemporary approaches.