Ayyy I missed this but I'll post since I saw it. Yeah Kelp Dome doesn't have many perches but it does have straightaways which sorta make up for it. Note these are S-rank tips
Here's quick map of the spots I see and use, and what they're used for, sort of in order:
1. popular starting position, you can shoot the guys coming off their shortcut over the wall. Other people use this a lot but I don't like it, maybe because I'm bad at seeing/shooting through the bottom of the grates. This spot is especially vulnerable to rollers, buckets, and blasters because you often have to extend onto the grate a little which reduces your mobility.
2. my preferred starting position. Lots of vision - enemy perch #1, enemy's flanking ramp, and much of mid - and a good ramp/platform to move around on. Watch your map to predict where enemies are going and what weapons they're using. Jump shoot the enemy snipers who come onto their position #1, they are often unaware of my presence.
Also a defensive spot if the enemy is pushing forward.
3. backup perch. Good vision but you're exposed as you hop onto this shortcut platform. There's no ramp to sneak up or jump shoot from. It can also cause traffic jams with your teammates who are just trying to get to mid
4. use pure range to shoot into mid. There isn't much cover here
5. corner peek spot so you can shoot into mid. Useful against enemy snipers who come over the shortcut
6. a mix of using range and corner peeking to keep people out of mid
7. more swatting people out of mid. Stay in your ink up here since there's no cover
8. pushing forward from mid, use range to hold off and pester the enemies while you and your teammates get to spot #9. Watch out for the enemy shortcutters
9. now you're really whooping them. Deny them the entire lane here, moving up as needed. Corner peek to avoid enemy snipers on the ramp directly in front.
10. way back at the beginning, this spot means you're either getting pushed back or a flanker is pestering you. Not much cover but at least you have range
11. you're really getting pushed back. Take jump shots if there are enemy snipers