You are quite right. In order to stage larger games we tend to use the following breakdown....
Each unit represent a regiment
Small unit 2 bases with 4 figures on each base
Normal sized unit 3 bases with 4 figures on each base
Large unit 4 bases with 4 figures on each base
The battlefield consist of two gaming tables with the size 180x120cm/6x4ft. The movement rate and ranges are 2/3 of the ones given in the Black Powder rulebook.