diff --git a/qhtcp-workflow/apps/r/calculate_interaction_zscores.R b/qhtcp-workflow/apps/r/calculate_interaction_zscores.R
index 0abb8d47..f9cbacf6 100644
--- a/qhtcp-workflow/apps/r/calculate_interaction_zscores.R
+++ b/qhtcp-workflow/apps/r/calculate_interaction_zscores.R
@@ -732,6 +732,8 @@ generate_interaction_plot_configs <- function(df, type) {
   delta_plot_configs <- list()
 
   # Overall statistics plots
+  OrfRep <- first(df$OrfRep) # this should correspond to the reference strain
+
   for (var in names(limits_map)) {
     y_limits <- limits_map[[var]]