diff --git a/Exec/science/gradient_detonation/README.md b/Exec/science/gradient_detonation/README.md
index a7bb2c57b6..837c5efbaa 100644
--- a/Exec/science/gradient_detonation/README.md
+++ b/Exec/science/gradient_detonation/README.md
@@ -8,7 +8,7 @@ A simple (carbon or helium) detonation.  The reaction network should
 be set through the GNUmakefile.
 
 This sets up a domain with a uniform density (dens).  A large
-temperature (T_ign) is placed in the accretion region with temperature T_l on the left side of the domain, and an ambient temperature (T_r) representing the WD core is in the right.  The transition from envelope composition to core composition occurs at the center of the domain, with the width of said region specified by delta. Finally, the parameter cfrac_core, nfrac_core, and ofrac_core, are the initial C12, N14, O16 fraction in the core, and the remaining material is He4. This is the same for cfrac_env...etc, which represents the material in the envelope.
+temperature (``T_ign``) with length ``hotspot_size`` is placed in the accretion region with temperature ``T_l`` on the left side of the domain, and an ambient temperature (``T_r``) representing the WD core is in the right.  The transition from envelope composition to core composition occurs at the center of the domain, with the width of said region specified by ``delta``. Finally, the parameter cfrac_core, nfrac_core, and ofrac_core, are the initial C12, N14, O16 fraction in the core, and the remaining material is He4. This is the same for cfrac_env...etc, which represents the material in the envelope.
 
 The left side and right side can optionally approach each other with a
 non-zero infall velocity, vel.
diff --git a/Exec/science/gradient_detonation/_prob_params b/Exec/science/gradient_detonation/_prob_params
index 4194964e16..19fb582b5c 100644
--- a/Exec/science/gradient_detonation/_prob_params
+++ b/Exec/science/gradient_detonation/_prob_params
@@ -1,9 +1,11 @@
-T_l                  real          1.75e8_rt        y
+T_l                  real          1.75e8_rt      y
 
 T_r                  real          1.e7_rt        y
 
 T_ign                real          1.75e9_rt      y
 
+hotspot_size         real          40.e5_rt       y
+
 dens                 real          1.e8_rt        y
 
 delta                real          50.e5_rt       y
diff --git a/Exec/science/gradient_detonation/problem_initialize_state_data.H b/Exec/science/gradient_detonation/problem_initialize_state_data.H
index d719e1aa86..646ef6308f 100644
--- a/Exec/science/gradient_detonation/problem_initialize_state_data.H
+++ b/Exec/science/gradient_detonation/problem_initialize_state_data.H
@@ -38,10 +38,10 @@ void problem_initialize_state_data (int i, int j, int k,
 
     Real temperature = problem::T_l + (problem::T_r - problem::T_l) * interp_factor;
 
-    if (i < 2) {
+    if (xcen < problem::hotspot_size) {
         temperature += problem::T_ign;
     }
-    
+
     // create a smooth transition from xn_env (left side of domain)
     // to xn_core (right side of domain)
     state(i,j,k,UTEMP) = temperature;