VHF/UHF vs 2.4GHz/5GHz
This is not the answer that you want to hear :-) :-(.
Propagation in buildings and tunnels and similar is complex.
During "911" they had disastrous results trying to use radios in buildings. A significant number of reports were written and they tended to conclude that around 800 Mhz was optimum. I read through the technical part of a number of these reports for essentially unrelated reasons* trying to find out the basis for their calculations. I found that all who gave a basis cited a single report that used a formula that was appropriate in its original context but randomly related to its use elsewhere. The parameter related to "roughness" of surfaces which tend to rotate the polarisation of the original wave with distance.
SO
You need to look at the equations for propagation and then decide what parameters are relevant and what they should be set to. 

Conclusion: Magic is required - there are too many variables with semi random values that vary case by case. Obviously (or luckily) there must be frequencies that work somewhat better in some typical sets of cases to be useful generalisations.



Not all the papers over time did as I claim above - but whether they are useful in practice is moot. Most deal with internal space as tunnels - buildings tend to be tunnels with reflective attenuators (aka walls) in them to increase the fun level. 

Here is one reference which comes to hand
ATTENUATION CONSTANTS OF RADIO WAVES IN
LOSSY-WALLED RECTANGULAR WAVEGUIDES 2013 31pp.

So you know what you're in for :-)


Abstract:  
At the ultra-high frequencies (UHF) common to portable radios, the mine tunnel acts as a dielectric waveguide, directing and absorbing energy as a radio signal propagates. Understanding radio propagation behavior in a dielectric waveguide is critical for designing reliable, optimized communication systems in an underground mine. One of the major parameters used to predict the power attenuation in lossy waveguides is the attenuation constant. In this paper, we theoretically and experimentally investigate the attenuation constants for a rectangular waveguide with dielectric walls. We provide a new derivation of the attenuation constant based on the classic Fresnel reflection coefficients. The new derivation takes advantage of ray representation of plane waves and provides more insight into understanding radio attenuation in tunnels. We also investigate the impact of different parameters on the attenuation constant, including the tunnel transverse dimensions, permittivity, conductivity, frequency, and polarization, with an aim to find their theoretical optimal values that result in the minimum power loss. Additionally, measurements of the attenuation constants of the dominant mode at different frequencies (455, 915, 2450, and 5800 MHz) for a straight concrete tunnel are presented and compared to theoretical predictions. It is shown that the analytical results match the measured results very well at all four frequencies.




Mother lode - maybe:

Here are references to a months plus solid reading while in self isolation. How useful they will be is tbd. This link will work after my PC next boots as Dropbox says it is not sinking at present. It is an RTF file containing 50+ live links and 30 or so citations - all of variable relevance.  

Tunnel {&amp;building} communications

I tried to use
bit.ly/tunnelcoms &lt;- please use
which allows me to see how many people accessed the link but the stupid SE system abhors such an equally good method (for reasons which are understood bu inlaid in cases like this one).
 People interested enough to look at the references would do themselves and me a favour by using the bit.ly link.