The key requirement to gain entry into the UK is you have to convince HM gov that they have a good reason to return home, therefore if thier employed, have money in the bank, own property. Easyvisa in Pattaya is run by a UK solicitor, they can help.
Yes its still a pain. The under consideration period, is needed for the home visit and outside of Bangkok your application is sent to Bangkok for approval. Do you have a Thai bank account?
The original problem was my lump sum arrived only a few weeks before my ext giving no time for seasoning, however in the end when immigration realised i want to switch my ext to support of a Thai child, they told me it just needed to be there on the day i put my ext in.