[Powers] Replacing Attribute roll with flat number plus talent

For a Supers campaign I'm starting up, I want to have a overall campaign rule that when powers require die rolls, they are instead usually based on 10+Talent, rather than Attribute+Talent (for example, for mental abilities that generally require an IQ roll such as Empathy). It seems to me like this should give a point cost discount as attributes are generally higher than 10 and players can pump the ones for abilities that they have. By the book, however, the only way that I can think to make it is with Cosmic: No roll required and Unreliable (10). This is a dramatic increase to the cost of the ability, however, which seems unreasonable. Any advice on how much such a change should cost? My hunch puts it at around -10%.

P.S. I am using multiplicative modifiers.

[Powers] Replacing Attribute roll with flat number plus talent