This…So much this.
Evocations aren’t very hard at all. You can even think of the name of the spirit, and it could come. It is as simple as manipulating energy. It is as simple as calling a name.
The most important factor is the input and the perceived result.
If you think doing something will have the result you want, do it, and it will, in evocation.
So basically you can imagine the requisite being whatever and when it’s met, the spirit being evoked.
Personally I just take their name and bring in the entity behind it. It’s usually instant.