[ns] what's the relationship of Pt_ and -txPower ?

[chen guoming]

Dear friends:
   We know that we can set different Pt_ and RXThresh_ to get different
transmit range. We also use energy model to calculate the energy used on
transimitting by setting -txPower. Then what's the relationship of Pt_ and
-txPower? Should Pt_ be greater than -txPower?
   During my simulation,I found I can set -txPower to a small value,for
instance, 0.025. However, I can still set Pt_ to the default value which is
0.281838 and it works fine. Than I am confused, if the power consumption of
Transmit is 0.025, how can Pt_ be so large?
   Anyone help me? Thank you for your suggestions!
Regards!
David