First_Medic wrote:

The deployment system in battle is a bit of a mystery and I haven't figured out the rules for reinforcement and support. Can you shed any light here?

In Stadia's OpenDev build, you had to research a tech to use reinforcement in battles. So if you haven't, that's probably why you were not able to reinforce your units.

Have you also reset the tutorial and set it to Beginner mode (Gameplay menu), that should explain you battles/combats mechanic in a more explanatory way ?

First_Medic wrote:
I generally like to set-up for a battle right where I am when I click the button to attack. Buuuuut the system immediately moves my units in advance of the deployment phase and I can't always get back to the intended position of advantage. I haven't detected any rhyme or reason to where they are placed either.

I would agree that combat mechanic is a bit obscure for a beginner (it was for me for the first OpenDev), but generally, if you're the attacker, you have the advantage of choosing the battle area (meaning you can hover your mouse over an opponent's unit on either sides of its hex tile), allowing you to visualize the best path according to terrain features. Then, after confirming battle, you'll be able to deploy on the best tiles you spotted before engaging into the battle.

If you still can join Stadia's OpenDev (which I can't anymore, so can't explain with screenshots), you should give it another try ;)