I would check with your IO or someone more knowledgeable than my self whether the rule of 2/3 months of 800,000/400,000 applies to the same account(s) at time of application/approval or is just any account that you hold that qualifies. I know it is unlikely (and nearly impossible to change banks if applied, but we all know Thailand's IO's (T.I.T.S!)
It is these little things that can trip us up with some IO's!