Sometimes I wonder if the game doesn't do any chicanery like checking to see how many you have before adjusting drop rates.
I can't imagine that. With my three TDC grind-rounds so far, I have searched with others in the cargo and found more.
My successful searches go like this:
1. Ship with Long Range Sensors, Limpet Controller ( in my case a Corvette or a Krait)
2. Entry at 20 km distance from Titan
3. Straight ahead full speed (without boost) into the centre of the Titan and through to the other side up to 15-20 km away
4. then circling around the Titan at low speed ( =full speed with cargo hatch deployed) at distances of up to 15 km for about 15 minutes
5. I collect materials and cargo along the way, mostly meta-alloys and samples
- I have usually already found a TDC by then -
7. if not, I fly out to 25 km away, turn around and repeat everything.
8. I boost very little so as not to miss anything
If I want another one directly afterwards, low wake out, turn and repeat.
(Low-waking out seems not necessary, as in one case I found two while circling).