diff --git a/crates/specialized/rtx-cfd/tests/embedded3_flag_wake.rs b/crates/specialized/rtx-cfd/tests/embedded3_flag_wake.rs
index 187c888..82f9dd1 100644
--- a/crates/specialized/rtx-cfd/tests/embedded3_flag_wake.rs
+++ b/crates/specialized/rtx-cfd/tests/embedded3_flag_wake.rs
@@ -388,8 +388,13 @@ fn flag_wake_on_the_device() {
         f
     });
     let vtk_dir = std::env::var("RTX_E3_FLAG_VTK").ok();
-    let phases = 32;
-    let last_period_start = t_end - period;
+    // `RTX_E3_FLAG_PHASES` phases per period (32); `RTX_E3_FLAG_VTK_FROM` = the period
+    // index the export starts at (the last period by default; 0 = the whole onset from
+    // rest, the viewer's sequence mode of 2026-09-22).
+    let phases = env_f("RTX_E3_FLAG_PHASES", 32.0) as usize;
+    let vtk_from = env_f("RTX_E3_FLAG_VTK_FROM", (periods - 1.0).max(0.0)) as f64;
+    let last_period_start = vtk_from * period;
+    let total_phases = ((periods - vtk_from) * phases as f64).round() as usize;
     let mut next_phase = 0;
     let mid = nz / 2;
     let slab = if slab_nz > 0 {
@@ -414,7 +419,7 @@ fn flag_wake_on_the_device() {
         let sample = (step + 1) % 10 == 0 || step + 1 == steps;
         let phase_due = vtk_dir.is_some()
             && t >= last_period_start + next_phase as f64 * period / phases as f64
-            && next_phase < phases;
+            && next_phase < total_phases;
         if sample || phase_due {
             device.download(&mut field);
             let solver = &device.solver;
@@ -506,7 +511,11 @@ fn flag_wake_on_the_device() {
             if phase_due {
                 let tag = if flag_span() >= duct_depth() { "full" } else { "free" };
                 let path = std::path::Path::new(vtk_dir.as_ref().unwrap())
-                    .join(format!("flag_{tag}_ny{ny}_phase{next_phase:02}.vtk"));
+                    .join(if total_phases > 100 {
+                        format!("flag_{tag}_ny{ny}_phase{next_phase:03}.vtk")
+                    } else {
+                        format!("flag_{tag}_ny{ny}_phase{next_phase:02}.vtk")
+                    });
                 write_vtk(&path, &field, Some(mask)).expect("vtk");
                 next_phase += 1;
             }