diff --git a/src/StaircaseShenanigans.jl b/src/StaircaseShenanigans.jl
index fd1675a..d172fdf 100644
--- a/src/StaircaseShenanigans.jl
+++ b/src/StaircaseShenanigans.jl
@@ -29,7 +29,7 @@ export STStaircaseInitialConditions, StaircaseICs, SmoothSTStaircaseInitialCondi
        PeriodicSTSingleInterfaceInitialConditions, PeriodoicSingleInterfaceICs,
        set_staircase_initial_conditions!
 
-export tanh_background
+export tanh_background, linear_background
 
 export AbstractNoise, VelocityNoise, TracerNoise
 
diff --git a/src/set_staircase_initial_conditions.jl b/src/set_staircase_initial_conditions.jl
index 476964b..d1b5cf0 100644
--- a/src/set_staircase_initial_conditions.jl
+++ b/src/set_staircase_initial_conditions.jl
@@ -24,6 +24,15 @@ function set_staircase_initial_conditions!(model, ics::STStaircaseInitialConditi
 
     return nothing
 end
+function set_staircase_initial_conditions!(model, ics::SmoothSTStaircaseInitialConditions)
+
+    # TODO: write methods to set smooth changes using the function provied in
+    # `ics::SmoothSTStaircaseInitialConditions`. I can use something like the above
+    # normalise then set with the smoothing function
+    #set!(model, S = initial_S_steps, T = initial_T_steps)
+
+    return nothing
+end
 function set_staircase_initial_conditions!(model, ics::SingleInterfaceICs)
 
     depth_of_interface = ics.depth_of_interface
@@ -45,15 +54,8 @@ end
 "Here the `BackgroundField` behaves as the `initial_condition` and noise is added to the
 tracer fields to create an instability."
 set_staircase_initial_conditions!(model, ics::PeriodoicSingleInterfaceICs) = nothing
-function set_staircase_initial_conditions!(model, ics::SmoothSTStaircaseInitialConditions)
-
-    # TODO: write methods to set smooth changes using the function provied in
-    # `ics::SmoothSTStaircaseInitialConditions`. I can use something like the above
-    # normalise then set with the smoothing function
-    #set!(model, S = initial_S_steps, T = initial_T_steps)
 
-    return nothing
-end
+"Fallback --- don't set any noise."
 set_noise!(model, noise::Nothing) = nothing
 """
     function set_noise!(model, noise::VelocityNoise)
diff --git a/src/staircase_initial_conditions.jl b/src/staircase_initial_conditions.jl
index 8c6661b..9a133e6 100644
--- a/src/staircase_initial_conditions.jl
+++ b/src/staircase_initial_conditions.jl
@@ -10,7 +10,7 @@ by a step change). The property `maintain_interface` is a `Boolean` which if set
 set [reentrant_boundary_conditions](@ref) so that the interface will be maintained (by not
 letting the system run down).
 """
-struct STSingleInterfaceInitialConditions{T, A} <: AbstractStaircaseInitialConditions
+struct STSingleInterfaceInitialConditions{T, A, B} <: AbstractStaircaseInitialConditions
     "The depth of the interface"
     depth_of_interface :: T
     "Salinity values in each layer"
@@ -21,7 +21,7 @@ struct STSingleInterfaceInitialConditions{T, A} <: AbstractStaircaseInitialCondi
                    R_ρ :: T
     "Boolean whether or not to set reentrant boundary condtions to approximately maintain the initial
     interface gradients"
-    maintain_interface :: Bool
+    maintain_interface :: B
 end
 function STSingleInterfaceInitialConditions(model, depth_of_interface, salinity, temperature;
                                             maintain_interface = false)
@@ -48,7 +48,7 @@ const SingleInterfaceICs = STSingleInterfaceInitialConditions # alias
 Sets a `BackgroundField` according to `background_State` and uses a triply periodic domain
 to evolve salinity and temperature anomalies about the background state.
 """
-struct PeriodicSTSingleInterfaceInitialConditions{T, A} <: AbstractStaircaseInitialConditions
+struct PeriodicSTSingleInterfaceInitialConditions{T, A, F} <: AbstractStaircaseInitialConditions
     "The depth of the interface"
     depth_of_interface :: T
     "Salinity values in each layer"
@@ -58,7 +58,7 @@ struct PeriodicSTSingleInterfaceInitialConditions{T, A} <: AbstractStaircaseInit
      "Initial R_ρ at the interface"
                    R_ρ :: T
     "Function used to define the background state about which an anomaly is evolved."
-     background_state :: Function
+      background_state :: F
 end
 function PeriodicSTSingleInterfaceInitialConditions(eos::BoussinesqEquationOfState, depth_of_interface, salinity, temperature, background_state)
 
diff --git a/src/staircase_restoring.jl b/src/staircase_restoring.jl
index 7ddabd7..a0a3910 100644
--- a/src/staircase_restoring.jl
+++ b/src/staircase_restoring.jl
@@ -160,7 +160,7 @@ function S_and_T_background_fields(ics::PeriodicSTSingleInterfaceInitialConditio
 
     ΔS = diff(ics.salinity_values)[1]
     Sᵤ, Sₗ = ics.salinity_values
-    S_parameters = (Sᵤ = Sᵤ, Cₗ = Sₗ, ΔC = ΔS, Lz = abs(Lz), z_interface, τ)
+    S_parameters = (Cᵤ = Sᵤ, Cₗ = Sₗ, ΔC = ΔS, Lz = abs(Lz), z_interface, τ)
     S_background = BackgroundField(ics.background_state, parameters=S_parameters)
     T_background = BackgroundField(ics.background_state, parameters=T_parameters)