Power Rail Routing Mastery: Multiple Voltage Planes in Altium

In S-G-S-S-G-S stack-up, if the core is 0.5mm and the rest is 0.1 would the middle signals still couple?

Will the impedance calculation change if you set the type of L2 (GND) as signal instead of plane in the stack up manager?
I usually use signal as my layer type instead of plane as i remember watching a video which show potential issues when setting it as plane.

Hey Zach! When people talk about digital signals transitioning between layers, having GND vias near the signal vias is generally a good idea. That idea I find gets lost when people talk about power. Daniel Beeker talks about it and from what I remember he calls it something along the lines of "water fall" vias. Tbh I forget exactly what he calls it.. :| I find most people just put an array of signal vias, enough to carry the current, but don't have any GND vias nearby. It was hard to tell with the example boards, but I did see some of that going on. I know it can be hard to get GND vias close by depending on the application. Do you think this is an actual problem that doesn't get attention? If so, what are some strategies you employ when delivering lots of power through layers on a board?