Equity Raising and Entitlement Offer

Hi, this is not another bull-or-bear up-or-down question. I'd like to run a sanity check on the entitlement offer by ANZ Bank (in Australian market). Full investor pack can be found here. TLDR version:

ANZ is buying another business and is raising capital via entitlement offer.

1. 1 new share for every 15 existing shares
2. Offer price is $18.90 vs last close $21.64

My understanding is, the maximum damage (share dilution) is 1/16 = 6.25%, which means as long as the share price is above $20.16, it will make sense to exercise the offer. Does it work like that? Or as long as the share price is above $18.90, I should just exercise?

I guess another way to ask the question is, does the share price get adjusted (similar to ex-dividend date) after these newly issued shares are added?

Thanks!