It is difficult for an architect to propose even a percent of construction cost fee for a project he knows little about. Any caveats he might add to a basic percentage would be for work beyond what he is normally asked to do or what he suspects you might want him to do.

I find that a percentage of the construction cost is a very poor way to establish a fair fee for the owner or the architect at any stage of the project.

The only way to know what any design work will cost is to define the scope of the project and ask for a proposal.

The 6% is an initial guesstimate. It likely means: "In my experience, when I get through with a fully custom design, the costs for architectural fees average about 6% of built costs. It could be more, or, if I use pieces of an existing design with maybe minor changes, it might be less."

When I have used architects, I have paid them by the hour, and that worked out fine. Depending on how much consultation was involved in the project's initial design, the number of revisions or changes, and the architect's involvement (or lack thereof) throughout the build, the cost for the architect could range from less than 6% up to 10-15%. I would never hire an architect who based his fees on what the rest of the project cost me. And responsible architects know that each project and client is unique, requiring varying amounts of time. If you want a satisfactory experience working with an architect, then you both need to be in agreement about how charges accrue. You wouldn't hire a plumber to put in a toilet who told you he charged 5 times as much to install a $500 toilet as a $100 one, even though the amount of work was the same. It should be no different with an architect.