I noticed a some discussion about Mantra

I understand verbal mantra to be tapas and generate heat. Is that correct?

For example a very precise Mantra that must be done in an exact way like Om namah śivāya in

Ghanapatha 108 times is definitely something that generates heat. (This is a very difficult mantra to perform correctly especially 108 repetitions)

and has its basis in pranayama rhythmic breathing

Would it be correct to say verbal mantra is Anavopaya?

Mental mantra is Shaktopaya i.e internalizing l?