OK, after passport control, you walk into the main hall. To get to the main THAI lounge, you would turn" left" and walk about 60 meters or so. If you keep on looking to your left, you will see a ramp that actually leads up towards the passport control for business class . Get to the top of the ramp, and then you take escalator down to the lounge.

When you decide to go to the gate for your flight, you can either take escalator up and again, and walk over the metal ramp and get back into the main building / shopping area. Depending if you are departing from" C" gate, or " D" gates, you would either walk to your left or right. The security check is done just before you get into that particular section of the terminal.
I have been through the new terminal four times so far.

Alternately, if you walk through the THAI lounge, you can get to " C" section without going up into the main shopping hall.

It really depends if you want any last minute duty free.
I came back on 18th December, and decided to do some last minute shopping at a shop located down near " C" security check.

Well, there was four rows of passengers, and it took 15 minutes to get through security. I was worried that I would not make the plane, and I had given myself plenty of time too.

I feel that if I had been under the main hall, I would have gone through security much faster. In future, depending on my schedule, I will do all my duty free shopping, and take the " underfloor " walk.

Its rather dark and gloomy , but, faster.

All the best................Peter