What's the equation for moon-moon tidal heating?

Between a moon and the primary, the equation for tidal heating is:

$$dot E_mathit{Tidal} = – Im(k_2) frac{21}{2} frac{GM_h^2 R^5 n e^2}{a^6}$$

But how does one calculate the tidal heating between moons?

Simplifying assumptions I’m fine with:

• The moons are coplanar, $I_mathit{affected} = I_mathit{perturbing} = 0$
• Both orbits have no eccentricity, $e_mathit{affected} = e_mathit{perturbing} = 0$ (which also implies no heating from the primary)
• The affected moon is tidally locked to the primary
• The perturbing moon can be treated as a point mass

While I’m not able to come up with any formula, I suspect the following properties hold:

• The tidal heating is still proportional to $Im(k_2)$, as this seems to only be an internal property of the moon.
• It’s still proportional to $R^5$
• Since tidal forces are inversely proportional to distance cubed, I think the overall heating is proportional to ${(a_mathit{affected} – a_mathit{perturbing})^{-3}}$, due to most heating happening while they are in close proximity.
• It’s inversely proportional to the relative synodic period of the two moons.