Not quite understand.
So every entry from a METV gives a 60 day stamp and every entry can be extended by 30 days (that you have pointed out.
As for back to back METV thinking that you could obtain one pretty much every year.
So something like 9 months in Thailand with a METV every year wash and repeat should be possible.
As you are aware an METV is only applied for in home country or country where you have permanent residency.
Some folk have asked about obtaining a METV using eVisa.
I cannot recommend that.