Thanks ID.
It's a toss up I guess, between 1:5 and 1:4. Only having 20 units is the problem - i.e. deciding what will be more 'game useful' overall. If I had 24 I'd almost certainly have 6 (1:4) and that would still leave me with 18 line.
Like my British and French I didn't go with any particular OOB, units in my collection just had to be in theatre sometime between 1809 - 1814. It was easier to do proportions with them because I did 28 close order 24 man (plus skirmish stands) infantry units for each army. Of those the British have five light (plus five smaller units of rifles and cazadores), the French have 8-10 units of legere - Hannovrienne and Du Midi are uniformed in line infantry coats and knee length gaiters so I can fudge them as line units if my needs require.
The Spanish sometimes put a lot of their cazadores battalions into a separate division, usually calling it the vanguard division or some such, and there seems to be a lot of them kicking about overall. I think I'll have to do five and add four or five more units (one more cazadores) to the collection at some point.
I also have a self made problem, regarding ratios, because of my game scale. I play army level games, with divisions as command groups where each 24 man unit represents 1,200 - 2000 men (each four stand unit has a strength value of 3-5 with 4 as the average, 400 men per point). At that scale, a typical British division (just over 5000 strong) is represented by three units; two 4 strength British units and one 5 strength Portuguese unit. When the game is being played, although each unit is actually brigade strength, units operate like battalions - which is what I've always called bath tubbing, though there seem to be various definitions of what that is. It does mean some fudging when it comes to ratios which is why line might be more useful in game terms. Ho-hum, it is what it is.