in a simple shunt-shunt feedback structure Transimpedance Amplifier, like a single stage push-pull amplifier with a passive feedback resistor, shown as following:

according the thermal noise analyse, to obtain low input rms noise current , i think it shoule maximize the resistor, and maximize L and minimize the W/L of the MOSFET to decrease gm and 1/f noise , but practically in my simulation and test, i found that it shoud maximize the resistor and W/L, and use minimum L. why the theory conflict with the fact?
hope someone help me solve this problem, thanks!