There are (too) many virtual keys (touch-and-hold to choose) in touch layout:
TH from key T,
PH from key P,
KH from key K,
CHH from key C (POJ),
TSH from key C (TL),
and all vowels with a diacritic
Virtual keys are slow to type.
There are still many unused keys (Q,W,R,D,F,Z,X,V) available to replace them.