I have to disagree with you all above as I have very recently discovered:
If you are mapping your iron+ball combination specifically for the approach shot then you must faithfully recreate that situation - that is from fairway to green, more so you must find the ideal green to shoot to - it should be dead level with the fairway and pancake flat.
Pancake flat is the only option unless you want purely distorted results on the roll-out, this also gives you a better idea in-game on how to adjust the predicted figure with the green at hand (e.g., if it slopes up from front to back you might want to add a couple of extra yards from the pancake flat derived predicted figure).
Only number 9 BPB (from the right side perimeter) can come close to idea (that I have found), and even then you will have to use a predictor to compensate the figure for any additional wind or difference in elevation between fairway and green for each of your irons.
And even then - you will have to fine tune your figures in game to give the best 'overall result' and to correct any spurious results you may have collected. And even then you will have to either apply a 'guestimate' correction factor for each green speed you are shooting on to or repeat the mapping on to every green speed (much prefer the correction factor method and it isn't much anyway - not enough to repeat all that work!!).
Map all your irons from tee-to-fairway and I will bet your long iron approaches will not be anywhere near as accurate as doing it this way.
Now you can all go and shoot me down in flames, lols - but I don't care because this is the way I am doing it these days and it is the right way to 'approach' it.