Thin CdTe detectors (3 X 5 mm2 electrode area and 0.5 mm thick), mounted in back-to-back configuration with common anode, have been characterized, aiming at determining the actual detection region with good spectroscopy performance. This geometry allows one to use devices with 1.0 mm useful absorbing thickness when irradiated in the classical Planar Parallel Field (PPF) configuration, and a large active area (3 X 1 mm2) and high absorbing thickness (5 mm) when irradiated in the Planar Transverse Field (PTF) configuration, while the charge collection takes place on maximum distances of 0.5 mm. These dimensions have been chosen on the basis of previous studies performed on various detectors irradiated in the PTF configuration which have shown that the 'best spectroscopy region' width assumes a constant value of about 0.4 mm in the thickness range 1.0 - 2.5 mm, while it is largely reduced when using smaller electrode area (2 X 2 mm2) 0.5 mm thick devices. The tests were performed by using a well collimated (0.1 X 1 mm2, 20 mm thick collimator) photon beam in the 10 - 300 keV energy range. The results concerning the spectroscopic behavior of both the coupled detectors and of single detectors (for comparison) have shown that the edge effects observed in smaller detectors with the same configurations are significantly reduced, giving better energy resolutions at Ex equals 122 keV, but no wider good spectroscopy regions; at low energies the effects of larger electrodes (increased electric capacitance and leakage current) result in a higher noise and increased detection threshold.