Most gyms have compliance to either or all of the following government agency's
1.sports authority of Thailand
2. Board of Boxing sport
3. Ministry of Education
Most embassy accept one of the above but sometimes they ask for a particular one, sometimes they want all 3 , sometimes they ask for business documents ( gym should be a Ltd company)
Like most things embassy related there is no set criteria.
Just try to find a gym with as much compliance certification as possible
if you border bounce every 6 months you don't have to buy more muay thai courses but if extend at immigration after 6 months you might need a new course
The feedback we have had from customers is that they are happy to convert long stay people to DTV they feel the visa was created for people who need to tidy up there visa record
So far people have had no problem re entering at CNX airport
They pull you to one side, which is scary, but simply as you to fill a form in which is mainly about where you are residing. Then they just stamp you in for 180 days
Re soft power we provide a brief curriculum and itinerary. We have a full curriculum drafted if they request, which we have only had once. The gym / school needs to provide as much information as possible to convince the embassy it's a well organized, accredited, professional institute who is registered for tax