Any 2 consecutive fixed weeks (0000 Mon - 2400 sun) must contain either 2 full weekly rests or one full and one reduced.
But that is not the same as saying you can only reduce every other, it’s quite complicated and won’t work for everyone and can only be done once before having extra time off to reset it.
You have a week off, start back at 0600 Mon, the last 45 hours upto 0600 count as a full weekly rest for that coming week 1, you work all week and take a reduced weekly rest, you then work all week 2 and take a reduced, you then work all week 3 and take a full, so you reduced 2 on the bounce then a full, but the actual fixed weeks were full, reduced, full.
It works by moving the rest that counts from the one at the beginning to the one at the end of the week. You need at least one min of holiday in week one, so if you started on Sunday it wouldn’t work.
You won’t be able to repeat this until you have a back to back weekly rest (90) that crosses midnight Sunday by at least 1 min, you’ll then keep this option of 2 reduced on the bounce so long as all your weekly rests cross midnight sun