It doesn't matter how "all different regionals" are handling the bonus, only how yours handles it, for you.

But since you asked, EDV includes our bonuses into our pay, so it's all covered on the W-2.

Bonuses are typically withheld at 25% at the federal level. The rest depends on your state and ALPA and other things held from your pay.

37.6% sounds a tad high, but it's hard to say, only you know your own tax situation.