Special rate pool-corporation

I was going through a question- Greenzone Ltd.

There the period-end was 6-month period to 31 March 2026.
And the company had installed new air-conditioning system for £550,000.

The question asks for maximum capital Allowances that can be claimed.

So the answer was 525,500

I was able to get it right but I was confused about WDA @ 6%

The answer explained that WDA will not be available on the remainder of the new expenditure until the following period.

Is it because we claimed AIA and FYA 50%?

And is this only for corporation tax?

Thank you.