short answer: The FA20 appears to have a 9 heat range, while the Lexus IS350 2GR-FSE engine appears to have a 6. A 9 is significantly colder than what you would find on an STi or a Supra from the factory.
more detailed answer: It's a Denso ZXE27HBR8 plug. That's a Denso 27 heat range... Denso uses different number range than the more commonly understood NGK system. Here's a conversion chart I found on sparkplugs.com:
The chart indicates the stock plug for the FA20 would be a 9 heat range on the NGK scale. When I first read that, I'll admit I'm skeptical. Now I haven't looked extensively at heat ranges for direct injected n/a engines. But I can't think of a mass produced passenger car engine using anything that cold when stock except with a rotary engine, and only then in the trailing position. I was thinking more along the lines of a 5 or 6 on the NGK scale as well. The coldest you'll see from the factory on even boosted engines is usually about a 7. You'd think it would foul out with a 9.
But here's something to consider. Do some Googling and you'll find that the 2GR-FSE engine in the Lexus IS350 (using an earlier version of the D-4S direct injection system) has a Denso FKB20H plug. If you cross-reference that with an NGK plug at RockAuto, it lists NGK spark DFH6B11A (6 heat range on the NGK scale). So that's two sources (including chart above) saying that an NGK 6 corresponds to a Denso 20.
So maybe the FA20 spark plug heat range is close to an NGK #9 after all.