10% is acceptable but it's also very much an arbitrary number. As well all know it's perfectly possible to start min-maxing parameters within 10% and get a bad weld.
Generally what I do is a targeted parameter range based off of some goal and science behind the joint. I usually throw 10% out the window and instead bound it based upon min/max heat input per inch. From there I start to design my secondary parameters. I don't know your product or weld enough to know what sort of tolerance you have 10% can be too loose or too tight.
I run quite a bit of DOE's, A good starting point would be a 3x3 and use Min/Max and Middle. you can probably remove 1 or 2 welds if you know they won't work. $50 isn't that bad for a macro a 3x3 would cost $450 bucks. Perhaps my idea of reasonable prices has been skewed, the mockups I'm working on are in the 6 digits... Please keep paying your taxes