I want the player characters to have lots of super-powers. For example, I want them to have inexpensive mental Modular Abilities with typically psionic abilities such as Psychokinesis and ESP and Mind Control (but no skills). Modular Abilities cost less if they are only mental. On the topic of Telekinesis, the main rulebook, page B92, says:
Psychokinetic: Your ability is part of the Psychokinesis psi power (see p. 256). This makes it mental rather than physical. -10%
I want to give the players all available savings, but I want to avoid double-dipping by giving the same discount twice.
In a normal campaign, level 10 Telekinesis would cost 50 points as a physical power, but 45 points as a Psychokinetic mental power.
Now let us suppose that the player characters start off with Modular Abilities, mental advantages only. Assume each mental advantage costs 45 points, and only one can be used at a time, so this power is a one-slot modular ability, base cost 5 points, slot cost 3 points per advantage point. $ 5+3\times45=190$ .
I think the basic cost should be $ 190-19=171$ , because the quasimoral power modifier deducts 10%. But I see in GURPS Supers, p. 46, that a wizard can have an extra 10% savings due to “mental advantages only” (i.e. no skills are allowed). So perhaps the basic cost of this mental slot should be 152.
[Question: which is more appropriate, 171 points or 152 points?]