Hole location equations

I am making an insert in a part. The part is parametric to the l,w,h. I would like to add some mount hole to the insert but they must be at 1" increments so that they can be used as CNC mount holes as well. SO I was hoping to make it so that the holes are at inch increments but do not go smaller than 1" apart. Most of that I can figure out(though help is welcomed) but I was curious if there is a way to make certain situations if the driving number for the size is not a whole number i.e. 4.5 or 3.25.

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