@propduffer
what you call independant sources is less than inofficial and called rumours. Nowhere has been any confirmation of the data you apply. Nowhere has been a release from Thai radars. Weather is not a factor for modern primary defense radar.
At 5000 ft a plane can go not faster than 330 NM ground speed (very optimistic). For half the way between IGARI and MEKAR it would lose 1/4 of its forward speed, which is 1/8 of the total route progress. This is at least 55 NM from a very conservative route length estimate (neglecting the 15 kts headwind and the lengthy turn after IGARI).
You may doubt the few hints that are published in official reports but believe the rumours from Malaysian newspapers, though.