We played a game of the Battle of Oriamendi at Drums yesterday. There were 7 players, 4 Isabellino and 3 Carlists.
I keep the Carlist reinforcements down to about 2/3rds of what they should have received to make the game a little closer in terms of both sides having a chance of winning. Other than that we had the right number of battalions for the order of battle.
The Carlists started with a little less than half the forces the Isabellinos had on the table. They were to receive almost as much as they started with in reinforcements.
When the reinforcements did show up they didn't really accomplish anything, 2/3rds of the infantry never deploying out of column and the cavalry shaking one unit of infantry but doing very little else except drawing 3 battalions away from supporting the assault.
The Carlists would probably have totally collapse if it hadn't been for the one Vizcayan battalion that took on all comers for about three turns before finally collapsing under the weight of frontal infantry and flank cavalry charges.
And shook both of those units assault it too.
While the Carlists did receive reinforcements they did the vast majority of the work with the forces that started on the table, taking on a force more than twice their size and holding out until both sides broke.
More pictures can be seen here:
imgur.com/a/E5EaH