A summoning on a metahuman would likely come across as a weird obsession though, and surely be detectable by Assensing. Unless it affects the 'astral form' only. There's several shadowtalk/'fluff' examples of a spirit answering a summoning taking longer than expected, even when there's nothing like background count interfering.
Oh, this made me think of a potential house rule (5e based, this would be too much in 6e I think):
- base number of rounds for a spirit to appear is equal to the number of its successes on the resistance test
- the caster may reduce that time by giving up service (each forgone service reduces the time to appear by one round. If the spirit rolled no successes, or the caster brings the delay down to zero, it shows up immediately).
- the caster doesn't have to stay summoning all of that time, it is still just a complex action, it is simply how quickly a spirit responds that is variable
I've long felt that spirits wouldn't feel quite so strong if they were not so cheap (action economy wise) to replace.
I have a team in Denver currently, and given GhostWalkers fraggery around spirits I think I may test run this to see how it feels. I'