My advice is not to worry about it and use the figures you have however based to play the game. The 4x2 figure firing line you will see in most 28mm games is an abstraction and not a strict reflection of the historic reality which varied across the 165 year period covered by the rules. In the early 1700s 4 ranks or more were still common, by the SYW and Napoleonic periods the norm was 3 ranks with some exceptions, by the ACW it was 2 ranks.?
I play Sharp Practice with my 15mm ACW figures which are based for other rules with 3-4 figures on a 1¡± base most in a single line. A base substitutes for a figure at 28mm scale so a Group is 24 figures and a Company in a Formation of 3-4 groups looks like a Company at 1:1 scale. It works very well.
Personally, I think the 2 figure deep firing line I can form by placing the bases in a 4x2 group looks good aesthetically for the ACW. Others have used multi figure bases where the figures are in 2 ranks which when placed in a group make it look like the unit is 4 ranks deep. You will find photos in the SP FaceBook group. I don¡¯t like the look myself but it makes absolutely no difference to play.
John?