I can't say why the recoat is giving you "better" results than the
first-time coat, but the Alodine/Iridite passivation treatment IS very
soft when it's first applied. It's never very abrasion resistant (it's
meant to be topcoated), but when it first reacts with the aluminum,
it's a watery gel. That's why the aluminum must be squeaky clean
before you treat it - water don't stick to oily stuff like
fingerprints.

Let the parts hand in the breeze for a day or two after you alodine
them, and they'll be as good as they get.

And remember, no aluminum Piper ever built, and damn few Cessnas ever
got alodined. You're gilding the lily in the first place....only the
Government (and mostly the Navy at that...) could ever afford to be
this picky about corrosion prevention.