Lower than expected current output from LT3465A

I'm using the LT3465A to power a string of 4 white LEDs in series. Vin is 5V, and the CTRL signal is a 3.3V PWM at 30kHz. The FB res is 1.6 ohm. Since the part has a FB voltage of 200mV I would expect 200mV/1.6Ohm = 125mA. I'm specifically interested in the case where the PWM signal is 100% duty (ie a constant 3.3V signal). I'm only getting about 150mV output across the FB resistor. I expect it to be 200mV. Any reason for the low output? Schematic and scope capture of FB resistor below.