Move alternative implementations (SFINAE) of a method to seperate file

I have a class with a bool as a template parameter to control the behavior of the class (in my particular case it controls whether or not a cache is used for certain calculations). All methods not affected by this option are defined in the .h file and implemented in a .tpp file. Though, one methods implementation depends on the passed template parameter and I am unable to figure out how I can move its implementation to the seperate file as well. Currently I have something similar to this example.

MyClass.h

template<bool enableCache = false>
class MyClass
{
public:
    MyClass() {}
    void someMethod();

    template<bool fwd = enableCache, typename std::enable_if<fwd>::type* = nullptr>
    unsigned int calcSomething() {
        // ask cache if calculation is necessary
        return 0;
    }

    template<bool fwd = enableCache, typename std::enable_if<!fwd>::type* = nullptr>
    unsigned int calcSomething() {
        // always recalculate
        return 1;
    }
};

#include "MyClass.tpp"

MyClass.tpp

template<enableCache>
void MyClass<enableCache>::someMethod() {
    // do something
    return;
}

This setup works (unless I introduced some minor errors while simplifying my original code), but I want to move the implementation of calcSomething to the .tpp as well. Can somebody help me with that?