12 tanks destroyed is a huge lose for most armies. Less missile but bigger ones means Pk is higher and guidance part is bigger and more effective.
Well another important point is that helicopters don't operate alone, so 12 ATGM per helo actually means 48 missiles per four helo flight group, which is plenty.
The best way to up the guided weapon count would be laser homing unguided rockets in rocket pods, as modern ATGMs have enormous warheads to penetrate very well protected MBTs which makes them serious over kill for the vast majority of actual vehicles on the battlefield like trucks and light vehicles... an 80mm rocket with a direct hit and a decent HE warhead would be perfectly fine for dealing with such threats...
Seems like Syria is a rather useful testing ground for them... and their attack platforms seem to be seriously benefiting from it.