Conversion to Flex

[donone]

I hope I am not being a nuisance, but I am finding it a little difficult to lay minimum semi-circles with Flex from Peco SL300 (i.e. when the length will be shorter than the original Flex length), The straight length will not reflect the final curve length so is difficult to predict. Using the radius and angle is perfect for the full length object or if I could predict the starting straight length needed for a final curve length. (I bet I haven't been very clear.)

In order to guide me I have laid Peco Settrack curves, when it occured to me that if I could click a button and convert that to Flex rather than try to follow it, problem solved. Would this be possible or desirable?
I feel sure there must an easier way.
I notice that sometimes Fled adjustment is not available but can't quite figure out when this is. Any help please.
Thank you 

[David]

No, don't worry, you're not a nuisance. We value all feedback.

But indeed, I do not fully understand!
You're trying to create a circular arc (part of a circle) from flex, right?

If you use the 'Curve flex' tool, you need to give a radius and an angle.
The length follows from that.

If you have a length of flex, and start to bend it with the control points, the length will obviously change.

If you mean to fill the space between two existing endpoints of to other pieces of track, simply drag one outer control point of the flex to the first endpoint, and the other to the second endpoint. The flex will line up properly by itself.

If you mean something completely different, please try to explain it again!

David.

[donone]

Not quite sure 
One example... not well explained.

I tried to lay a flex curve for half circle or something near to, and was restricted by the angle dialog to 90 deg. The flex being 1 metre long would mean a cut to make 2 x 90 deg or say 90 deg plus 80 deg then join them.

I actually needed to end up in a certain place but not to fill a specific gap between tracks. I needed the next section that will eventually join, to be horizontal, so the finish angle was sort of fixed in its approach to the point aimed at.
I do not actually know the angle required though I know the minimum radius.
To overcome this I laid several SetTrack sections and arrived at the correct place but had difficulty trying to lay a piece of flex to match and then replace the SetTrack. So I am using the SetTrack as a template if you will.
I want these sections to be one piece as far as possible.

Maybe I am going about this in the wrong way.
When the angle is set, is it absolute or is it relative to something, like the current position of one end or something, because the dialog is always zero to start?

[Edit] I am homing in...
If I set a track to say 23 deg I can calculate the required remaining angle to get to a required angle and therefore set the dialog to deal with this. However, if I forget the original angle (after about 30 seconds with me) or if I originally set it by eye then I don't know the angle and so cannot calculate the new curve. If I could click on the curve and have it tell me the angle from say horizontal, I could then calculate the rest.

[Edit +] Just discovered the picture export etc. Does this explain better than my huge dialogue?
That didn't work, I can't see how to get the picture onto the reply