I still use bolt + rivet and can never get the stream on the popcorn enemies at the end of s1 and I think thats cause of the ship I choose. Still have yet to hit 20mil (highest is 17) but I've read that it's much easier when you unlock the loop.
Hmm, gave this combo a little bit of practice yesterday, not an easy one. I forgot how much slower it takes Rivet to ignite gems. But I was able to pull the stream at the end of stage one. Are you possibly not maxing the rank out by the end of the stage? As in the popcorn enemies returning a solid stream of bullets (like you see in my videos) when they turn around?
Basically, you want to start the stream on the line of tanks when they get to the bottom left side of the screen, then start tapping forward quickly with the stick to keep the stream going. Making constant small movement is really the trick with pulling gem streams.
I'd even suggest switching to Nail if you feel up for it, she's the best pair with Bolt and she can ignite gems much quicker than Rivet can going by my play yesterday. Plus, she moves faster which is not as jarring as the speed decrease that you get with Rivet, especially using Bolt.
With the final section of stage 3's boss, if you can't point blank him it like I do in my video's, try the strategy I use in my 72 mil run. It was the first way I found to successfully beat that pattern. There's actually a third way to tackle that pattern, and it's what I use on 2-3 in my near-ALL playthrough, which is basically staying to the left side and just moving up and down in the pattern. You can perform this technique on the first loop as well!
The rest of the sections just require a little practice, like the intro to stage 5. The midboss on that stage can get point blanked to death easily, wish that same strat worked on the second loop...