conversion losses FET resistive fet mixers

i am using down converter FET resistive mixer. RF power is negative i.e RF power = -10dbm, when i varies LO power from +5dbm to +10dbm the conversion losses increases i.e from -20db to -5 db.

is it ok? i mean is it working properly bcoz the conversion losses increasing....

You need to have high enough LO power to turn the fets from full on to full off. Your 5 dB loss is quite respectable. Diode ring mixers are about 6 dB and the theoretical limit is about 4 dB.