Atomization enthalpies of transition elements

So, my book says that transition elements have higher enthalpies of atomization than other elements (say s- or p- block) because of stronger metallic bonding, primarily due to large number of unpaired electrons in the d-orbitals. 


Now, if that is the case, then the atomization energy for $\ce{Ni}$ should be less than for $\ce{Fe}$ and $\ce{Co}$, as $\ce{Ni}$ has only 2 unpaired electrons compared to $\ce{Fe}$ and $\ce{Co}$ (4 and 3 respectively). 


Actually, it is just the opposite.


$$\begin{array}{cc}
\text{Metal} & \Delta\_\text{atom}H(\ce{M})\text{ / }\mathrm{kJ~mol^{-1}} \\ \hline
\ce{Ni} & 430 \\
\ce{Co} & 425 \\
\ce{Fe} & 416
\end{array}$$


Why could this be?




These sorts of generalities always sweep aside other considerations.


$\ce{^26Fe}$ has a ​body-centered cubic crystal structure.


$\ce{^27Co}$ has a ​hexagonal close-packed crystal structure.


$\ce{^28Ni}$ has a ​face-centered cubic crystal structure.


Here is a [nice table](https://www.webelements.com/periodicity/enth_atomisation/) showing the overall trends.


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According to J.D.Lee's "Concise Inorganic Chemistry", the extra electrons in the metals of the 2nd half of the transition series, like Fe, Ni etc.. are excited to the p level .. and then the unpaired electrons in the d, s and p levels participate in metallic bonding .. so Ni has the max. unpaired electrons, followed by Co and then Fe ... and hence strength of metallic bonding follows same order


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