I have the 48" radius platen from Bill Behnke. I use it for chefs S grinds. But it's definitely too subtle a hollow grind for narrower knives. Even the 36" radius would not work. You'd need max 12" radius(24" diameter wheel equivalent) I believe, but such a platen would build heat very quickly, if it ever exists.
For your needs, better stick to the standard rubber contact wheel IMO...I know the larger ones are expensive, but you save a lot of cleanup time because the rubber backing is great for use of fine and structured abrasive belts.