Around 6 years ago, my followers began using the term “sweet spot” in reference to the load that they felt maximized their glute activation during hip thrusts. I had very strong clients who could hip thrust 315lbs for 5-10 reps, however, they felt their glutes working the most when they used 185lbs. Naturally, they wanted to know whether they should stick solely to their sweet spot load or go heavier, even though they didn’t feel their glutes working as much.
My advice is to use a variety of loads and try to get your glutes to feel all of them. I remember when I hip thrusted 815lbs, my hamstrings almost seized up and I barely felt my glutes working at all. That said, I am able to feel my glutes working very hard with a legit 3RM and 5RM. And of course, with anything above 10 reps.
Oftentimes, you cannot feel your glutes because your form deteriorates. This is not always easy to detect, but you don’t achieve as much hip extension (less glutes), you arch your back more (more erectors), and you push more with your legs (more adductors, hammies, and quads). If you’re stricter during heavier sets and at the end of lighter sets, you will feel more glutes.
Nevertheless, it’s okay to use your sweet spot load most of the time. A good rule of thumb could be to use your preferred weight with 60% of your sets, with the remaining 40% split between going heavier and going lighter.
Variety is good, and you should experiment with different set and rep schemes as well as tempos (pause reps, etc.). The goal is to gradually raise your hip thrust sweet spot over time, with a big emphasis on gradual. It won’t go up by 100lbs in 2 months; think more like 20lbs every 4-6 months, and the rate of increase diminishes with more years of lifting experience.