It may have had something to do with the lower cost of maintaining regiments in Ireland and staying within the limits of the Irish Establishment which had been set by The Augmentation Act of 1769 [mandated that the garrison of Ireland be 15,328]
So more regiments stationed there but with lower establishments. In early 1793, a quick count gives 16 cavalry and 14 infantry regiments in Britain [excluding the Guards] and 12 cavalry and 23 infantry regiments in Ireland. There were also a number of regiments on the Irish Establishment but serving in the colonies.
The establishments were used to determine how much money would be necessary in a 365 day period to maintain a regiment. The full amount was requested in the estimates. I am also thinking that the establishment would be used to determine the allowances granted to each Colonel to clothe his regiment, etc., as well as, for the government to provide the great coats, etc.
In the extraordinary expenses of the army in a given year, Colonels were granted additional money to defray their costs if an augmentation was granted during the year. I believe expenses were covered for any reduction in the establisment as well, but not so certain on this one.
You are of course, quite correct, in that regiments hardly met their establishments unless a second battalion was drafted into a first battalion and the second was sent home to recruit.