Recommended value for this ItrendLevel is the following:

between 0.10 and 0.16 for usdjpy M15 (I prefer 0.16); 
0.19 for usdjpy H1;
0.19 for H4.


0.0017 - 0.0026 for gbpusd M15 (I prefer 0.0026); 
0.0044 - 0.0050 for gbpusd H1;
0.0044 for H4.


0.0013 - 0.0017 for eurusd M15 (I prefer 0.0016 or 0.0017); 
0.002 for eurusd H1;
0.002 for H4.

0.0015 for usdchf M15; 0.003 for usdchf H1,
0.003 for H4.


You may find you own settings:
Attach iTrend indicator to the chart. 
This indicator is counting everything 
up to 300 bars back on the history 
starting from the current bar.
And you may see the value of Itrend 
(see image f1.gif). Then shift your chart 
on 300 bars back and during the 
shifting you may estimate the 
maximum (see image f2.gif). 
Then multiply this max by 0.283. 
The resut is ItrendLevel.

I want to note that if you are trading 
using m15 timeframe you need to estimate 
ItrendLevel at least once per two days, 
for h1 - one time per week. And because 
of that the backtesting results are not valid 
(we are backtesting using permanent 
ItrendLevel value but it is subject to change).