You are right with that statement....
I have acros that only encrust and refuse to grow vetically,
some would churn out growth at incredible rates.....
some jus simply refuse to grow and stay stagnant.......
Majority of the acros have shown growth except for these 2....
pink staghorn and the purple monster......
On the positive side, have a Montipora digitata thats giving me growth rates ap to 2 times within a 6 weeks period.....