"---folks in the BOI are just "weeding" out anything that would cause their bosses to have to figure whether or not some document or letter was valid
documentation for the qualifications. Too much explanation could cause even more problems. Documentation needs to be clear and fits with their expectations. Good luck."
This excerpt from Prenock's message elsewhere in this string succinctly states the way BoI officials operate. The bosses who approve the applications have a set of criteria they stick to. Permutations of the required documents and variations of different kinds impose additional work of evaluations and decisions. They do not like that. For example, they understand the American 1040's include all income sources and are very straight forward in terms of gross taxable income and taxes, thereby indicating clearly the net income. They may have similar criteria for other countries.
There is also a matter of personnel dynamics in BoI. The officials one interfaces in the office are not the ones who make the final approvals, but are mere intermediaries. I found this out when I tried to get a statement next to my LTR visa stamp that I am exempted from health insurance because of the $100,000 deposit in an account. ( I felt I needed this because Immigration often ask me for health insurance proof when I arrive in Phuket). The BoI official I met was very empathetic, but after going back and forth to meet his boss four times, finally came back with a firm statement that no such statement can or need to be written because: 1) Immigration is not supposed to ask for health insurance for an LTR, and 2) the LTR regulations specify that the 100,000 deposit is sufficient in lieu of health insurance.