I used a Wilson Sleek for many years. The instructions with my Wilson Sleek stated that the antenna needed at least a 4 inch diameter metal base. So I attached a custom piece of sheet metal a little over 4" diameter to an extendable pole that I erected when camping. It worked fine. So to answer your question, as far as I know, the size of your metal base mentioned should do the job just fine.
Last year I moved up to a WeBoost Drive 4G-X, a vastly superior cell signal booster, also from Wilson Electronics. Re the Wilson Sleek, keep in mind that those are out of production and should you need replacement parts for them, you can't always find them.