^^ Unfortunately, this seems to have been true for some but not for others. Regardless of magnitude (within limits), tax on Interest from accounts designated as "saving" has traditionally not been implemented identically to that from accounts designated as "fixed deposit" . But it appears that "the times they are a changin".
As an analogy to post 2635 but with a twist, I suggest caution regarding the current Thanachart "ultrasaving" account scheme. This proposal at first view looks “relatively” favorable however, although seemingly unmentioned on website, and possibly also at application, opening an account with a passport (but seemingly not an id card) results in immediate tax deduction for any interest. Apparently in force for a long time already.