It can vary slightly from club to club in the set due to the tolerances and sole radius. 1″ would be the general dimension. The best way to insure the proper club lengths is to trim the shafts for flex (parallel tip only) or install the taper tip shaft that matches the head number and then cut to the laying length from the butt. That way you eliminate worrying about slight variances in the bottom of the bore to the heel dimension. The variances are so slight, generally a millimeter or less, there is no effect on the flex of the shaft. You can dry fit the shafts to the heads after trimming the tip (if necessary), insuring they are to the bottom of the bore, cut to length, then install with epoxy. Or, you can simply cut the tip (again, if necessary), install with epoxy and after curing cut to the final playing length from the butt end.
I know you probably know this already, but trying to calculate the bottom of the bore to the heel dimension on every iron in a set is time consuming, requires a club gauge and very precise measurement that in the end will not yield any improvement in the build or the performance. More important to be precise in the shaft trim and overall length measurements and trim.