Historical theatres encompass diverse architectural typologies whose influence on spatial acoustic parameters has not been systematically quantified across building types. This study presents binaural and lateral energy measurements at 52 receiver positions in five European theatres spanning three architectural subtypes: traditional horseshoe with enclosed boxes, modified horseshoe with open continuous galleries, and a modern rectangular proscenium auditorium. Linear mixed-effects models were used to separate the fixed effects of seating zone from random variability among venues. Seating zone had a highly significant effect on IACC and LF (p < 0.0001). IACC exhibited a binary spatial distribution, with Stalls Front positions approximately 0.17–0.20 higher than all other zones, which were mutually indistinguishable. LF followed a gradient across four seating levels, increasing from Stalls Front through Stalls Rear and Lower Boxes to Upper Boxes. Architectural typology, rather than room volume, appeared to explain inter-venue IACC differences most clearly. The single modern rectangular theatre exhibited IACC values approximately 2.5 times higher than all other venues, a difference attributable to its flat specular surfaces and rectangular plan rather than to room volume (Spearman rank correlation: ρ = 0.10, p = 0.87). The theoretically expected negative correlation between IACC and LF was confirmed within the horseshoe theatres (r = -0.38, p = 0.009) but was suppressed when the rectangular theatre was included. These results show that specular lateral reflections can decouple IACC and LF, with implications for acoustic assessment in typologically diverse performance spaces.