diff --git a/qhtcp-workflow/apps/r/calculate_interaction_zscores.R b/qhtcp-workflow/apps/r/calculate_interaction_zscores.R
index 71064ce6..00301b10 100644
--- a/qhtcp-workflow/apps/r/calculate_interaction_zscores.R
+++ b/qhtcp-workflow/apps/r/calculate_interaction_zscores.R
@@ -739,6 +739,7 @@ generate_interaction_plot_configs <- function(df, type) {
 
     for (var in names(limits_map)) {
       y_limits <- limits_map[[var]]
+      y_span <- y_limits[2] - y_limits[1] 
 
       # Common plot configuration
       plot_config <- list(