LC oscillator harmonic balance simulation in hspice

i want to simulation effect of changing tail current on amplitude of negative resistance LC oscillator. when i change tail current from 1mA to 3mA, the amplitude do not change! i use harmonic balance simulation in Hspice. my technology is .18um. but when i use transient analysis in Hspice, the amplitud is changed!
i don't know what is it problem. please help me!
this is my netlist:

.option post
.option method = gear
.param lmin=0.18u
.probe hb i(mna)
.probe hb i(mnb)
.probe hb i(mn1)
.probe hb i(mn2)

.HBOSC TONE=1G NHARMS=10 PROBENODE=2,3,1 FSPTS=20,0.5G,1.5G
.probe hbosc v(2)
.probe hbosc v(3)
.PHASENOISE v(2,3) DEC 20 1k 100MEG METHOD=0 CARRIERINDEX=1
.probe phasenoise phnoise
*****************Voltage************************** **
vdd 1 0 dc 1.8v
*************Current****************************** **
ibias 1 5 dc .002
mna 5 5 0 0 nch l=lmin w='100*lmin'
mnb 4 5 0 0 nch l=lmin w='100*lmin'
*********************Teransistors***************** **
mn1 2 3 4 0 nch l=lmin w='200*lmin'
mn2 3 2 4 0 nch l=lmin w='200*lmin'
***********************L&C************************ **
l1 1 2 2nH
l2 1 3 2nH
c1 1 3 12.5pF
c2 1 2 12.5pF
************************************************** **
.end