Janna E with Trist E

I've been playing a lot of Janna recently, and I've found myself wondering how the interaction between Tristanas e and the AD boost from jannas E works. If I shield trist after she's stacked up an E on someone, but before it explodes, does the explosion damage go up, or does it depend on the AD at the time it was stacked?

If it does benefit the explosion damage, is it actually worthwhile to do so? Or would the extra AD benefit the AA's used to stack the E charge more than the E itself would benefit? Or does the math work out that it's the same either way? (I'm mainly thinking relatively early game, where Trist won't have enough AS to reach 4 stacks and detonate the charge early, and so the shield will expire before the detonation occurs if shielded at the onset of the e placement.)

While in practice it's probably moot, as trist is probably going to be under fire and so want the shield early on for the shields sake rather than the AD, but I am curious how it works in theory.