Actually the percentage matters much less than people think (it's almost a marketing thing at this point imo). The actual parental sizes matter a lot. There are 75% SD females that are still over 12'. There are also 25% SD females that are under 8 foot. While percentage comes into play some, the actual genealogy and lineage of the animal matters much more. I have a 50% female who is 4 years old, healthy and fed well and she is maybe 7.5 feet, give or take a few inches. I have personally seen a 68.75% female that was ~13 feet. Whereas I have a 25% SD that was produced by Garrett Hartle that is almost 8 months old, fed a large meal every 5-7 days, and is probably 2 feet (still smaller than a male mainland hatchling as I have those too). And he is 25% Kayuadi at that, which is considered more "dwarf" than SD overall. So when you are shopping for SD's, make sure to find out the size of the parents, their age and their feeding schedule. You will thank yourself in the long run, trust me.
Just for reference, here is a picture of me with my 50% SD female GC Het Purple. As you can see, she is still very manageable (I am 5'7" for reference), being less than 8 foot and already breeding size and age. She is a F1 cross at that (mom was a pure SD ~7-8 foot and dad was a pure mainland GC Purple Albino that was ~7 foot). This is an example of what I mean when I say parental sizes matter more than percentages. There are also some with the field of thought that the babies tend to get more of the size from mom and the looks from dad.
P.S. I was doing a monthly mouth inspection as I do with all my retics to make sure everything looks in order (no signs of pushing, stomatitis, RI etc.). So please don't mind how I am holding her head. It looks rougher than it was.