How do you use True/False User Parameters in the iPart Author table?
To answer to your question...
In the iPart Author dialogue on the "Suppression" tab you will find what you ask for.
Click on it and it will appear on your table below the name of the feature as suppressed or not, depends on the statement that is active... (if that is not the case use the middle arrows by selecting the appropriate feature to transfer it on the right block as shown in the picture...)
Check Pic & Model
If you ask my opinion!!! ;)
The one cancel the other (iLogic the ipart) so I don't really understand the usage of the iLogic here...
However the results that you ask for are coming by a published iPart (No iLogic) in your Library or Even better by publishing the profile in frame generator!!!
As can been seen the parameter it is available but on a different way
After playing a bit... more flexible by custom parameters for Length and Miter Angle
And.... here it is the dialogue to suppress, change angle and length of course if you publish that in your library will look much better like below...
I believe you are looking on something like that if you choose iPart...