Why not just give the Walker relatively large feet for it's size? I've seen the Mobile Propulsion Labs (A group dedicated to constructing a real life mecha) perform calculations showing a 4 Ton Mecha 20 feet tall (Granted this thing had no armor) with feet large enough to practically walk on quicksand, far lower ground pressure than human feet have. You don't have to use normal human proportions, just give the thing snoshoes and you're good to go through a guy's lawn without damage.

Yep, not like those 50 foot wide strips of pavement we need for cars.

That's really the point. The only advantage that humanoid mecha have over cars is agility. A mech can go places where a can't. It can maneuver in tight spaces in a way that a car can't. Ideally, it can step over obstacles. Having giant feet kind of defeats this advantage, without which a mech is just an absurdly expensive, vulnerable, and slow car.