You need a new base factor. So, your smallest 2θ is giving a ratio of 1, you now need to change that to a ratio of 2. The Miller indices will change from 100 to 110. Now you can calculate a new base factor by taking sin2θ/2 This is new base factor. Then divide your sin2θ for the 1.5 ratio and you should then get an integer or close to integer value.