diff --git a/tests/test_config_flow_pairing.py b/tests/test_config_flow_pairing.py
index 8497956..2849f6e 100644
--- a/tests/test_config_flow_pairing.py
+++ b/tests/test_config_flow_pairing.py
@@ -28,6 +28,20 @@ from nsh.const import (
 _KEY_PATH = "/tmp/nsh-test-adbkey"
 
 
+_STUB_NAMES = (
+    "voluptuous",
+    "homeassistant",
+    "homeassistant.config_entries",
+    "homeassistant.core",
+    "homeassistant.helpers",
+    "homeassistant.helpers.entity_registry",
+    "homeassistant.helpers.selector",
+    # Loaded execution runs beneath the stubs; never escape this file either.
+    "nsh.helpers",
+    "nsh.config_flow",
+)
+
+
 def _install_import_stubs() -> None:
     """Register import-time stand-ins for HA/voluptuous (idempotent)."""
     if sys.modules.get("voluptuous") is not None:
@@ -139,6 +153,25 @@ def _flow(user_input_host: str, monkeypatch=None):
     return flow
 
 
+@pytest.fixture(autouse=True)
+def scoped_stubs():
+    """Contain the import stubs to this module's tests (t7 INFO).
+
+    Snapshots every injected sys.modules entry and restores or removes it on
+    teardown, so later tests never observe the fake homeassistant/voluptuous
+    (nor the stub-loaded nsh.helpers/nsh.config_flow) modules.
+    """
+    snapshot = {name: sys.modules.get(name) for name in _STUB_NAMES}
+    _install_import_stubs()
+    yield
+    for name in _STUB_NAMES:
+        original = snapshot[name]
+        if original is None:
+            sys.modules.pop(name, None)
+        else:
+            sys.modules[name] = original
+
+
 @pytest.fixture
 def mocked_test_connect(monkeypatch):
     from nsh.connection import ShieldConnectionManager
diff --git a/tests/test_connection.py b/tests/test_connection.py
index d59034f..8131182 100644
--- a/tests/test_connection.py
+++ b/tests/test_connection.py
@@ -211,15 +211,22 @@ class TestReconnectBackoff:
         manager = _manager(poller)
 
         delays = []
+        backoffs = []
         backoff = 5.0
         for _ in range(7):
+            backoffs.append(backoff)
             delays.append(await manager._watchdog_cycle(backoff))
             backoff = min(backoff * 2, 300.0)
 
-        # 5→10→20→40→80→160→300 growth with easing; the last must not exceed
-        # the cap (with jitter).
-        assert max(delays) <= 300.0 * 1.25
-        assert delays[1] >= delays[0] * 1.5
+        # F5 soundness: the previous ±25 % jitter could flake the claim
+        # delays[1] > delays[0] * 1.5: BACKOFF=10 jittered to 9.17 vs
+        # BACKOFF=5 jittered to 6.25 → 6.25*1.5 = 9.375). Assert only what
+        # jitter guarantees: each delay sits inside ITS OWN backoff's band
+        # (non-overlapping consecutive bands ⇒ delays[1] >= delays[0],
+        # since min next = 7.5 >= max first = 6.25), and never above the cap.
+        for backoff, delay in zip(backoffs, delays, strict=True):
+            assert 0.75 * backoff <= delay <= 1.25 * backoff
+        assert delays[1] >= delays[0]
         assert delays[-1] <= 300.0 * 1.25
 
     async def test_repeated_failures_do_not_spam_listeners(self):