Try to record the tape at as high a volume as possible without distortion to maximize auditory range. Eastern Screech Owls have two primary vocalizations, a descending trill and a monotonic trill. Both are present on some commercially available bird call recordings. The descending trill is thought to be a territorial defense call used mainly in late summer and fall, while the monotonic trill is considered a nest-site advertisement and family contact call, and is heard more in early spring and summer. I have used each of these calls alone, and interspersed, and I seem to get better response when both calls are present.
All variants work well, however.
The presence of these alarm calls seems to enhance attraction of other species to the mobbing flock. Both techniques are used by birders to attract birds, and will work well even without owl vocalizations. Many birding supply companies sell small mechanical squeakers of wood and pewter that produce a variety of chirping and squeaking sounds. These sounds will also sometimes bring birds in closer than they would come with the owl tape alone. The use of taxidermic mounts of screech owls or even simple model decoys may enhance photographic opportunities even more, as it would give the birds a specific focus for their attention.