Lets see if I understand
group ratio is the factor in *equal* divisions of an interval, such as an octave.
prime example being 2^(1/12) = 1.05946309 is the ratio between semitones in 12 EDO (standard western tuning)
Then... group size is how many times this set of X repeats?
A couple thoughts here.
Alternative solution => I think the (real) .TUN format specifies the frequency for each of the 128 midi notes. Scala can export those files as well and perhaps this would be easier to implement?
Working with .SCL files
I think the interpetation of the scala file needs to be expanded. What the scala file gives you is an example octave (or whatever period). So there are three things missing as far as I can tell.
1. a true tuning origin - C 5 is the usual I see - when I tried changing this in OMPT even weirder things happened.
2. Repeating + tuning overall interval. For example:
19 out of 36-tET, Tomasz Liese, Tuning List, 1997
The 2/1 indicates an octave - the tuning needs to be repeated tuning, tuning + 2/1, tuning + 2/1 +2/1, etc.
3. the tuning needs to be read backwards from the origin in a manner like the above statement except tuning - 2/1, tuning - 2/1-2/1, etc.
In the next post I will post a "true" .TUN format, which like I said might be easier to implement.