How can we physically define reynold number variation in terms of characteristic length?
The freestream Reynolds number ($Re_c$) of the wing and hstab would be different due to different chord lengths:

$$Re_c=\frac{\rho_\infty V_\infty c}{\mu}$$

where $\rho_\infty$ is the freestream air density, $V_\infty$ is the freestream airspeed and $c$ is the reference chord (of the wing or hstab). I'll discuss the physical significance of reference chord below.

1. Viscous drag

The physical significance on drag is best understood from the flat plate Blasius solution in laminar flow. The overall friction drag coefficient ($C_f$) decreases as a square root of freestream Reynolds number:

$$C_f=\frac{1.328}{\sqrt{Re_c}}$$

So the longer the chord (i.e. higher Re), the less significant the boundary layer viscous effects are to the overall drag. This is further illustrated in the graph below.



Image ref: https://www.sciencedirect.com/topics/engineering/friction-drag-coefficient

Take note, however, that the dimensionalized (total) friction drag still grows since $C_f$ here is non-dimensionalized with respect to the reference chord, $c$.

2. Turbulence transition

Increasing the chord doesn't increase the momentum thickness in absolute terms. However, the relative thickness with respect to the chord is different for different chord lengths:

$$\theta(s) = \frac{0.664\sqrt{\mu}}{\sqrt{\rho_\infty V_\infty}}s^{1/2}$$

where $s$ is the chordwise position from the leading edge.

Since natural transition is a function of the momentum thickness Reynolds number (Ref. Drela, Flight Vehicle Aerodynamics), which increases with respect to the momentum thickness, transition to turbulence will occur at similar chordwise location, $s$, in absolute terms, but earlier in relative terms ($s/c$) for the longer chord.

This has the effect of increasing the stall angle of attack for the larger chord, manifested in the effective increase in the freestream Reynolds number.