Creating non-contiguous groups in Designer

[GordonFAffinity]

I'm a fan of using groups to organise layers in Designer. However I've come across a situation where that doesn't work, because it seems that grouped layers have to be contiguous. I have a diagram where I need to show one layer behind others, to create a depth effect. I'm attaching a screenshot to show what I mean. In this diagram the "collars" around the frame contain multiple parts, two of which need to appear in front of the frame and one behind. If I try to group these parts (layers) together so that I can organise them the back layer gets promoted to the front, which kills the effect. Am I missing something? Is there another way to achieve the effect I'm trying to achieve? TIA.

[GarryP]

Welcome to the forums.
All of the layers in a group will be rendered at the same ‘level’ within the document in respect to the other document layers.
Some layers within the group will be higher/lower than others in the group but they will all be rendered below the layer which is above the group and above the layer which is below the group.
I don’t think there is any way to change this.
To get what you want (if I have understood correctly) I think you will need to create two groups, one for the layers below and one for the layers above.

[Alfred]

Not that it makes any difference as far as the front/back grouping question is concerned, but does the front of the “collar” really need to be in two parts? The gap next to the base of the triangle looks like an error.

[GarryP]

Here's a ‘cute’ way to create the arrow part of the ‘collar’.
* Create a Rectangle;
* Convert to Curves;
* Select the Node Tool;
* Create two nodes by clicking anywhere on the vertical sides (position doesn’t matter);
* Drag-select the middle nodes on the vertical sides;
* Open the Transform Mode (on the Context Toolbar);
* Make sure Show Alignment Handles is ON;
* Click the Vertical Centre Alignment handle;
* Drag what’s selected to the left or right (you may need to alter your Snapping options to make this easier).
See attached video.
It’s not particularly amazing, but it might come in useful to some people.

[Alfred]

28 minutes ago, GarryP said:

Here's a ‘cute’ way to create the arrow part of the ‘collar’.

Very cute, Garry, but if you don’t need that much adjustability you can simply align two diamonds with the sides of the rectangle and then Boolean ‘Add’ one and ‘Subtract’ the other.

[GordonFAffinity]

Both of these suggestions are clever, and I probably wouldn't have thought of the first one and clearly didn't think of the second!

As far as my original question is concerned, I appreciate the quick response from GarryP. I'm not surprise that this isn't possible, since it seems to me that layers are a fairly fundamental part of Designer. (And Gary, thanks for pointing out the apparent error. The top half of the collar doesn't need to be in two parts: I just haven't got round to combining both yet).

I wonder if my problem could be solved if objects (possibly layers) were associated with a "set". I could then leave the grouping as is, but associate each component with the set "collar". That would give me the organisation I'm looking for whilst still leaving the objects themselves in their current layers. I appreciate I need the layers to get the effect, but I only want to connect the objects to keep them clearly associated in the layers list. This is a feature request, I suspect, and so not something that ought to be raised here, but maybe someone sees another solution with this prompting?

Again, thanks for the very helpful responses and suggestions. Much appreciated.