Here is my simplified understanding:
Depends on the ratio you need. Since people are finding success with 49:1 ratios that means you need to wind 1 turn on the primary to 7 turns on the secondary. Or, 2 turns on the primary and 14 turns on the secondary (14/2=7, 7 squared = 49) and so on.
In your example the turn count of 5/2 has a ratio of 6.25:1. (5/2=2.5 2.5 squared = 6.25) Make your secondary winging 14 turns will give you a ratio of 49:1. I'm certainly no expert on ununs but as I understand the theory of design you divide the secondary turn count by the primary turn count and then square the result to get your final ratio.
@prcguy, feel free to offer corrections or comments if my understanding is flawed.