I'm not a radar tech person, but I would assume (hope)that the radar has a 100% efficient reflector to make the radar waves transmit forward. If for some reason the reflector is not 100% efficient, some radar waves may move backwards (or any other direction). Now, if the cabin pressure bulkhead behind the radar does not stop radar penetration, then some radar waves may enter the cabin. Clearly, the further back you are, the less exposure.

This is more an academic statement and I have no proof so would welcome clarification.

But again, why would I care whether radar penetrates the cabin?

Microwave ovens cook because the frequency of the radiation in the magnetron excites (vibrates) molecules in the food. Radar uses a similar frequency to that in your domestic microwave (but is very effectively shielded to stop that radiation escaping). If you choose to stand in front of a ships radar, you will be badly burnt and possibly die if you don't get out of the way quick enough. You will be cooked (ie burnt).

Now, aircraft radar backscatter would be trivial compared to the radiation in front of it, but I am curious how much actually does go backwards and into the cabin. For all I know, it may be so slight that it hardly is measurable at all. Cosmic radiation (from outer space) may be a much greater hazard (and that IS documented as a hazard to crew).

My vote is for seat 2 A or K. 1 A and K just feels a bit too close to each other. But if I am travelling with my spouse, then would definitely opt for 1 A or K and then the joint seat in the middle as a second choice.