Essentially heel toeing with your right thumb...

👍👍
Indeed you have put a lot of thought into it...
I wish I could do the same...
Lol kinda. Regardless of button layout, it’s still a semi-automatic sequential transmission, so you don’t need a clutch, therefor no heal-toe downshifting required.
If you want to be technical, what that layout allows for is what I would refer to as a “poor man’s clutch kick”. Most of my time spent drifting was done with people using wheels, with clutches. This allowed them to be able to clutch kick, an essential technique in drifting, especially in low powered cars. DS3/4 users don’t have access to this, so the best we could do is mimic a clutch kick by holding the Hand Brake and Gas at the same time. Keep the Gas held down when you release the Hand Brake, it acts like a poor man’s clutch kick.
Used it a lot doing big reverse entries into corners like Grand Valley T1&2, Deep Forest T1, etc. Fly down the straight in top gear, Scandinavian Flick to initiate the drift, then drag the Hand Brake to maintain angle while using the Foot Brake to slow the car down (I used to run my Brake Bias really far forward, so the Foot Brake only effects the front, and then the Hand Brake is your rear brakes). Keep the Gas to the floor the entire time, while downshifting into 2nd/3rd/4th, whatever gear is desirable to be in for mid corner. Once you reach the turn in point, release the Hand Brake, which will induce instant wheel spin (thanks to the throttle being fully applied). This causes the car to stop sliding in a straight line, and start turning into the corner. The lower the gear you go down to, the tighter the car will want to turn in. If you don’t do this technique, at best you’ll look un-smooth, at worst, the rear will grip up when you release the Hand Brake, usually causing nasty snap-back.
I’ll never claim to be the best, and I wasn’t very good in comps...but I got smooth enough using a controller for drifting that majority of people I met in lobbies just assumed I was using a wheel.