It doesn't matter if the washer is higher.
I used to put the top of the box at 48" because it was a natural break for the drywall.
We sometimes drain a washer into a laundry tray, which is even lower.
You need a long enough standpipe for a washer to prevent overflow.
804.1 All plumbing fixtures or other receptors
receiving the discharge of indirect waste pipes shall be
approved for the use proposed and shall be of such
shape and capacity as to prevent splashing or flooding
and shall be located where they are readily accessible
for inspection and cleaning. No standpipe receptor for
any clothes washer shall extend more than thirty (30)
inches (762 mm), nor less than eighteen (18) inches
(457 mm) above its trap. No trap for any clothes
washerstandpipe receptor shall be installed below the
floor, but shall be roughed in not less than six (6)
inches (152 mm) and not more than eighteen (18)
inches (457 mm) above the floor.