Pulse phase thermography (PPT) is widely used for non-destructive testing of fiber reinforced polymers. Shades occur when inspecting three-dimensional (3D) specimens with a single flash lamp, but can be circumvented by using a transmission setup (TM). In this contribution, PPT is applied to a 3D specimen with artificial defects in TM and compared to reflection mode (RM). The artificial defects consist of PTFE and aluminum foil and are varied in position, size and depth. Reflector surfaces are constructed to enhance the thermal stimulus on the specimen’s slants in TM. The specimen-dependent construction method is presented. Using the reflectors leads to a higher contrast between defective and sound area. Ampli- and phasegrams provide complementary information in TM, motivating a data fusion approach to improve defect information. Hit rates and detected defect sizes between RM and TM with and without reflector are compared. Overall, TM combined with reflector usage leads to the highest hit rate, whereas detected defect size deviations are smaller in RM. Especially deeper defects and defects on slants are more reliably detected in TM.