All of the rotary wing Army Sqn have been 12 aircraft, with the exception of 161 and 162 Sqn with Tiger*. They are 8 aircraft Sqn, and were always intended to be.** It has ended up as two Tp of 4 aircraft which has worked well; but has also led to a culture of viewing attack helo support as Tp's, not as Sqn like you do with utility helicopters. That poses interesting restrictions on the Bde Comd being supported and a reasonable amount of stress on the maintainers and aircrew. The idea that you are only going to have 2 - 4 helicopters (generally) supporting on any given day reduces the ground scheme of manoeuvre options - an extra four airframes can now allow that Sqn to have 6 - 8 helo's up at any given time - much better support
Adding to this is the readiness cycle. With only 16 airframes (noting that some of those are in deeper maintenance), it's hard to maintain a Sqn or Tp at the readiness levels needed, just because of the small number of airframes. Keeping 4 helo's ready from 8 (with their crews and other support elements) is harder than 4 from 12 - especially as (like all enabling Brigade), 16 Brigade doesn't have the depth for a reset Sqn.
Overall, 12 aircraft Sqn are better deployed, ready, on exercise or in barracks.
* this all ignores CH-47 - there just isn't 12. But it's a good example of the different thinking and restrictions aren't an airframe issue, but a numbers issue.
** note that they were to be 8 aircraft Sqn of Tiger, Apache or Cobra - although with more airframes in the fleet of Tiger v the other two (so the above would have been even harder, from a numbers point of view).