diff --git a/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/poisson/device_cg/setup.rs b/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/poisson/device_cg/setup.rs
index 94d2798..6d7d87f 100644
--- a/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/poisson/device_cg/setup.rs
+++ b/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/poisson/device_cg/setup.rs
@@ -1,5 +1,5 @@
 //! R6-3: the moving path's Poisson setup on the device (`e3_pset.cu`),
-//! behind `RTX_E3_POISSON_DEVICE=1` (default off). From the projection
+//! default ON (`RTX_E3_POISSON_DEVICE=0` restores the host setup). From the projection
 //! tables `DeviceCut` holds (step apertures, open flags, activity, owners,
 //! the merged cells' CSR) the operator (`Solver::poisson_operator` with
 //! `merge_small_cells`), the fine level (`Level::new`: activity, masked
@@ -81,10 +81,10 @@ fn kernels() -> &'static PsKernels {
     })
 }
 
-/// `RTX_E3_POISSON_DEVICE=1` (default off).
+/// Default ON (`RTX_E3_POISSON_DEVICE=0` restores the host setup).
 #[must_use]
 pub fn enabled() -> bool {
-    std::env::var("RTX_E3_POISSON_DEVICE").is_ok_and(|v| v == "1")
+    !std::env::var("RTX_E3_POISSON_DEVICE").is_ok_and(|v| v == "0")
 }
 
 /// `struct PsGrid` in e3_pset.cu.
diff --git a/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/cut.rs b/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/cut.rs
index 63685b9..c72cc6a 100644
--- a/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/cut.rs
+++ b/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/cut.rs
@@ -909,7 +909,7 @@ impl DeviceStep {
             // w, p (fresh cells take their neighbours' pressure) and the
             // previous velocities (the imposition's source).
             let mut field = self.host_field.take().unwrap_or_else(|| Field::new(g));
-            // R6-3 (`RTX_E3_FIELD_P_ONLY=1`, default off; not under the band
+            // R6-3 (default ON, `RTX_E3_FIELD_P_ONLY=0` off; not under the band
             // check, whose references read the whole mirror): the download
             // waits until the step's rebuild route is known — with the device
             // classification and imposition the host rebuild reads and writes
@@ -1101,7 +1101,7 @@ impl DeviceStep {
                 self.cut.as_ref(),
                 super::poisson_setup::device_grid(&self.solver, g, dt),
             ) {
-                // R6-3 (`RTX_E3_POISSON_DEVICE=1`): the operator, level, lists,
+                // R6-3 (default ON, `RTX_E3_POISSON_DEVICE=0` off): the operator, level, lists,
                 // links, components and export on the device from the step's
                 // projection tables; `RTX_E3_BAND_CHECK=1` hands the host
                 // operator as the reference.
@@ -1144,7 +1144,7 @@ impl DeviceStep {
                 smoother: self.solver.params.poisson_smoother,
                 ..MultigridParameters::default()
             };
-            // R6-3 (`RTX_E3_POISSON_DEVICE=1`): a moving body's hierarchy with
+            // R6-3 (default ON, `RTX_E3_POISSON_DEVICE=0` off): a moving body's hierarchy with
             // level 0 built on the device; the host build otherwise (or when
             // the hierarchy would stop at level 0).
             let device = match (self.solver.is_moving(), self.cut.as_ref()) {
diff --git a/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/poisson_setup.rs b/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/poisson_setup.rs
index e236985..6ac442c 100644
--- a/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/poisson_setup.rs
+++ b/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/poisson_setup.rs
@@ -1,5 +1,5 @@
 //! R6-3: when the moving path's Poisson setup runs on the device
-//! (`RTX_E3_POISSON_DEVICE=1`, default off) and its grid description.
+//! (default ON; `RTX_E3_POISSON_DEVICE=0` restores the host) and its grid description.
 
 use crate::solvers::incompressible::embedded3::Grid;
 use crate::solvers::incompressible::embedded3::poisson::device_cg::{
@@ -53,9 +53,9 @@ pub(super) fn device_grid(solver: &Solver, g: Grid, dt: f64) -> Option<OperatorG
     })
 }
 
-/// `RTX_E3_FIELD_P_ONLY=1` (default off): the rebuild's field transfer
+/// Default ON (`RTX_E3_FIELD_P_ONLY=0` restores the full transfer): the rebuild's field transfer
 /// limited to the pressure when the classification and the imposition ran on
 /// the device.
 pub(super) fn field_p_only() -> bool {
-    std::env::var("RTX_E3_FIELD_P_ONLY").is_ok_and(|v| v == "1")
+    !std::env::var("RTX_E3_FIELD_P_ONLY").is_ok_and(|v| v == "0")
 }