Make sure that when you record, your screams are coming from the diaphragm as opposed to the throat! Good posture is key !! Really, the same rules for recording any kinds of vocals apply. Doubly so to maintain your throat health! If you have a limited space where you can't stand up, or even sit up straight, arching your back as straight as possible helps push out screams a little better/ more effortlessly. Take a good few breaths before each scream. If you need an extra oomph for the screams, try like... hmm the only way to describe the phenomenon is by like having your body /push/ out the scream? I noticed I sometimes had to lean forward to give my screams power/depth, if that makes sense?
Good old voice preparation techniques help, I can't stress enough, like the one that works very well for me is where you sing open vowels while arching your tongue so that the tip of your tongue is behind your bottom teeth and your tongue is almost touching the roof of your mouth. I can't find a video on that though :' ((
Make sure you place the mic/mic gain at a comfortable distance from you/setting so your samples don't clip either
As for vibrato... that's interesting, I feel like I have an idea what you're talking about but I'm having a hard time imagining how it'd be affecting screams that much ! It might just be good for the output.