There is some information on backgrounds in French data.
Not admittedly Ireland but does perhaps offer some pointers.
The recruits before 1792 were mainly from urban areas, despite 80% of the population being non urban. The proportion of NCOs from urban areas was even higher.

It would seem more the pressures on those who had given up the land had little alternative if they fell on hard times in an urban area than join the army.

In Ireland it may be worth looking at the pressures forcing people to leave the land to find your answer. Large increases in urban population without accompanying new factories would suggest a surplus ready for the army, as would regular famine.

Jeff Lewis