How to force unit formation during battle setup?

Units can be organized into custom formations, however this doesn't always work. Especially with artillary the unit order is often changed:

1. Arrange the unit cards in the right order.
2. Form the units into a group.
3. The order is changed to what I'll call the 'background' order.
4. Force a different order by dragging a unit card and dropping it on the group to move it to the end. If you do this in the right order, you can force the order.
5. Now the unit card order is respected.
6. When moving the units around the card order is not respected, instead the background order is used.
7. When the grouping is removed, the unit cards revert to the background order and abandon the forced order, which is what normally does happen.

Again, in most cases I can form a custom order and send units into battle respecting that order. This problem seems to occur when artillary is mixed with infantry. Here's a screenshot of this happening with a group of two bolt-throwers, White Lions of Chrace and Lothern Sea Guards. My custom order is:
Sea - Lion - Bolt - Bolt - Lion - Sea
The order when I click and move the units around is:
Bolt - Bolt - Sea - Lion - Lion - Sea

So it seems the artillary is pulled out, while otherwise the order is respected.