Visa exempt entry generally is for a short term vacation or limited function. Doing so 5 times in succession, with some short hops out, isnt really what the system is for. Not too surprised immigration officials are wary of intention. Try to get an appropriate visa for your reasons to spend so long in thailand.
I guess its all about balance of hassle and costs ...for me a non imm o retirement extension works well, being in thailand maybe 8 months a year, I have the money in thailand and the relative loss in interest cost (high interest uk account vs low interest thai account) is about 8000 baht a year, but means I have relatively easy and cheap (1900 baht) in thailand annual extensions, no repeated applications to an embassy, no to and fro to a border. Horses for courses.
I did ...but my reply was perhaps a prompt to revisit that option as non imm o (not oa which they may have considered) ...my view being ...best option Tod
Non imm o with retirement extensions ...easy and flexible and gives range of options for visits ...the fact the visa is for 12 month extensions is kinda irrelevant ...
you will need 800,000 baht in a thai bank account for several months prior to applying for your 1 year extension on your 3 month non o visa obtained in the uk
they check thru luggae yes, but thought had to exit domestic and go thru intenational security departures ...where the desk is for rebentry permit. Will have to try it sometime ...not done for years!!! 😘