OK, the sun came out, but there were no aluminium-painted roofs handy, so I had to make do with wet blacktop.
Here are the readings to interpret as you wish:
Incident meter directed straight at the sun: f/11½ (no surprise!)
Spot meter reading off wet blacktop: f/64½
No matter which way I pointed the incident meter, the highest reading I could get was f/11½.
Meter set at EI 100, 1/125 second. Clear sky, slight haze. 2 pm, New York.