This is the crux of the issue that the first post describes. I think the problem is that a lot of brewers don't understand what they're trying to do: a session IPA should not be your normal IPA with the original gravity cut. The mash profile for most American style IPAs favors a highly fermentable wort; in my opinion a session IPA should arrive at a lower ABV not just by lowering the grain bill and OG, but also by lowering the fermentability of the wort by altering the mash profile. This is why those session ales in the UK are so delicious; they have a wonderful malt backbone in the finished beer and haven't been fermented so dry that the only thing left is hops and alcohol (their malt also tends to be just a little bit less modified than American malt - that reduces fermentability a little as well). If you are using a brewing calculator and you just plug in that you want 4.5 ABV instead of 6.5, all it's going to do is tell you how much to cut the grain. It's not going to tell you to alter the mash profile or maybe pick a different yeast strain with lower attenuation. The brewers that are making excellent session ales picked up that extra bit of knowledge somewhere. The hop portion, ironically, is probably the easy part.