When you do a dummy booking, carry on until you get to the "review your flight details", then look down at the "price" section, and click on the "fare basis information". The first letter of the fare basis is the fare class

Looks like:

Super Flexi Deal books into Q
Sweet Deal books into V
Flexi books into H

One Way Flexi books into B
One Way Sweet Deal books into M

Just a point to note, on my LHR-AMM route, the wide body A330 was replaced with a narrow body A321.

RJ business is great - cannot comment on economy

In terms of maximising TPs, the simple rule is that you need your trip to break down in different segments with each segment having a different flight number. Also segment over 2,000 miles are considered long-haul and earn more TPs

Kingfisher (IT) and BA will fly direct so it is only one segment over 2000 miles so you earn 70TPs (35TPs for discounted economy) one way
Flying RJ means you have to change planes at AMM and LHR-AMM and AMM-DEL/BKK are both segments over 2000 TPs so you earn 140TPs (70TPs for discounted economy) one way. AMM is well positioned for ex-LHR/AMS flights on RJ
If you chose Finnair (AY) instead, you would only earn 40TPs + 70TPs = 110TPs (20 TPs + 35TPs = 55TPs for discounted economy) one way since LHR-HEL is less than 2000 miles

RJ is the best airline to maximise TPs when flying eastwards