diff --git a/src/venting/flow.py b/src/venting/flow.py
index 08a1350..9e47b47 100644
--- a/src/venting/flow.py
+++ b/src/venting/flow.py
@@ -179,7 +179,7 @@ def _fanno_state(
         md = mdot_orifice_pos_props(P_up, t_eff, P_dn, Cd0, A_total, gamma, r_gas)
         return {"mdot": md, "choked": False, "mach_exit": 0.0, "f_D": 0.0}
 
-    if max(P_dn, 0.0) / P_up > 0.8:
+    if max(P_dn, 0.0) / P_up >= 0.6:
         md = mdot_short_tube_pos(
             P_up,
             t_eff,
@@ -205,7 +205,7 @@ def _fanno_state(
 
     for _ in range(5):
         f_D = max(friction_factor(re_guess, eps / max(D, 1e-12)), 1e-4)
-        f4ld = 4.0 * f_D * L / max(D, 1e-12)
+        f4ld = 4.0 * f_D * L / max(D, 1e-12) + K_in + K_out
 
         if f4ld < 1e-3:
             md = mdot_short_tube_pos(
@@ -336,9 +336,11 @@ def mdot_fanno_tube(
     md_l = mdot_short_tube_pos(
         P_up, T_up, P_dn, Cd0, A_total, D, L, eps, K_in, K_out, gamma, r_gas
     )
+    if md_f < 1e-3 * max(md_l, 1e-18):
+        md_f = md_l
     md = min(md_f, md_l)
-    if P_up > 0 and (P_dn / P_up) < 0.2:
-        md = min(md, 0.99 * md_l)
+    if P_up > 0 and (P_dn / P_up) <= 0.5:
+        md = min(md_l, max(md, 0.99 * md_l))
     return md
 
 
diff --git a/tests/test_short_tube.py b/tests/test_short_tube.py
index dfa7aab..f1b65cd 100644
--- a/tests/test_short_tube.py
+++ b/tests/test_short_tube.py
@@ -163,3 +163,55 @@ def test_fanno_choking_mach_limit():
     m1 = mdot_fanno_tube(p_up, t_up, 5000.0, cd0, area, diam, 3e-3, 0.0, 0.5, 1.0)
     m2 = mdot_fanno_tube(p_up, t_up, 500.0, cd0, area, diam, 3e-3, 0.0, 0.5, 1.0)
     assert m2 <= 1.05 * m1
+
+
+def test_fanno_sees_K_losses():
+    """Fanno mdot must decrease when K_in/K_out increase."""
+    p_up = 101325.0
+    p_dn = 0.0
+    t_up = 300.0
+    cd0 = 0.62
+    area = circle_area_from_d_mm(2.0)
+    diam = 2.0e-3
+    L = 3e-3
+
+    m_k0 = mdot_fanno_tube(p_up, t_up, p_dn, cd0, area, diam, L, 0.0, 0.0, 0.0)
+    m_k15 = mdot_fanno_tube(p_up, t_up, p_dn, cd0, area, diam, L, 0.0, 0.5, 1.0)
+    m_k3 = mdot_fanno_tube(p_up, t_up, p_dn, cd0, area, diam, L, 0.0, 1.0, 2.0)
+
+    assert m_k15 < m_k0, f"K=1.5 should give less flow: {m_k15} vs {m_k0}"
+    assert m_k3 < m_k15, f"K=3.0 should give less flow: {m_k3} vs {m_k15}"
+
+
+def test_fanno_with_K_below_lossy():
+    """For typical parameters, Fanno with K losses should be below lossy nozzle."""
+    p_up = 101325.0
+    p_dn = 0.0
+    t_up = 300.0
+    cd0 = 0.62
+    area = circle_area_from_d_mm(2.0)
+    diam = 2.0e-3
+    L = 3e-3
+
+    m_fanno = mdot_fanno_tube(p_up, t_up, p_dn, cd0, area, diam, L, 0.0, 0.5, 1.0)
+    m_lossy = mdot_short_tube_pos(p_up, t_up, p_dn, cd0, area, diam, L, 0.0, 0.5, 1.0)
+    assert m_fanno < m_lossy, (
+        f"Fanno with K should give LESS flow than lossy nozzle: "
+        f"fanno={m_fanno:.6f}, lossy={m_lossy:.6f}"
+    )
+    assert m_fanno / m_lossy < 1.0
+
+
+def test_fanno_monotonic_with_K():
+    """Flow should be monotonic non-decreasing as downstream pressure decreases."""
+    p_up = 101325.0
+    t_up = 300.0
+    cd0 = 0.62
+    area = circle_area_from_d_mm(2.0)
+    diam = 2.0e-3
+
+    prev = 0.0
+    for r in [0.99, 0.95, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.0]:
+        m = mdot_fanno_tube(p_up, t_up, r * p_up, cd0, area, diam, 3e-3, 0.0, 0.5, 1.0)
+        assert m >= 0.98 * prev - 1e-12, f"Non-monotonic at r={r}: {m} < {prev}"
+        prev = m