[namada]

The simple method would be to require higher levels of wealth for knights rather than this special case rule. Historically, knights were incredibly wealthy individuals, after all, owning some of the most expensive gear available at the time - just looking at Europe, a typical knight would have a horse (very expensive, tremendously so in the case of the finest warhorses), a battlefield suit of armor, and a ceremonial suit of armor (far more lavish & expensive than the other). That's not even getting into lands, servants, and weapons.

Of course, knights typically also carry a host of Patrons and associated Duties too, so don't forget those. And much of their wealth comes in the form of inherited lands which produce a profit, which might be better represented as Independent Income, rather than raw Wealth levels.