The terminology used is 'share holder' / shares. Starting with the fact that most Thai Registered Companies (Co.,LTD.) have one - usually two Thai partners who are designated in the Company Certificate as owning 51% of the shares. That leaves 49% to divide up. Plus it most often means 2 to 4 additional Thai employees for every additional foreign share holder. This may not apply to BOI companies.
You go to the U.S. Embassy Website - find Consular Service - download the Income Affidavit Form. Go to another area a click away and make an appointment - read the rules. No Proof - just your passport and the form stating X Dollars each month. Raise right hand and swear pay $50.00 in USD or Baht
Income Certificate / Embassy Income Letter / Embassy Income Affadavit = 65,000 per month obatined at the U.S.Embassy in Bkk.
No need to have a Thai bank account. Just swear by signing a document which is notarized at the Embassy Notary Section. You swear - no proof - needed that you have income in USD from the U.S. monthly that meets the equivalent upon exchange of 65,000 baht
For employees getting an alternate 12 month multi-entry B Visa in Penang instead of the one year extension of stay at immigration is no longer possible. The 20% share factor I read about is rare - if ever.