I don't know the particular scent I'm afraid but I assume it is much like most aftershaves versions of quality scents, which is, as you say shorter lived with a lower percentage of "the good stuff" to alcohol.
I would generally take the edt version given the choice but I can see how it has been a great buy for you at the price.
You can try spraying less of the edt and giving yourself a good dose of AS to make your edt bottle last much longer and you should also get more of a "symphony" of notes (albeit for less time).
There are even certain scents that I think are "better balanced " in the aftershave versions, (Cerruti 1881 springs to mind). Also some vintage AS is quite strong enough not to need to bother with EDT version. I have Givenchy Gentleman vintage which is wonderful, bought for about £5, for example which to me is way better than the current EDT.