Electrocardiographic imaging (ECGI) allows evaluating the complexity of atrial fibrillation (AF) signals using the Boundary Element Method and Tikhonov regularization. An accurate ECGI reconstruction is dependent on a proper selection of the regularization parameter (λ). In this work, two ranges of λ are explored to evaluate the effect of λ on the quality of the ECGI reconstruction. ECGIs of 20 AF patients were computed using zero (T0), first (T1) and second (T2) order Tikhonov regularization (TR) for two ranges of λ: from 10^-9 to 10^2 and 10^-12 to 10^-4. Dominant frequencies (DF) and the number of rotors obtained with the two ranges and methods were compared. Zero-order Tikhonov showed to be more robust in λ selection for different λ ranges. For lower λ ranges, higher DF was found (T2, p<0.05) and more rotors were detected for T1 and T2 (p<0.01). Differences between TR methods compared by λ ranges showed more variability in derived metrics for lower λ range (p<0.01). Optimal ranges for λ search differ among T0, T1 and T2. Election of lower than optimal λ values result in an increased estimated electrical complexity.