I tried to do that.... but to be honest, it is one of the features that sometimes works for me, and sometimes doesnt. Might be me...
I send in Federic (the army) and the column in question from Dresden to Pirna, in a coordinated move (estimated time 6 days). I also send in a column from the east (across the river) (eta 4 days).
The column from Dresden arrived first in Pirna, and retreated at once. No battle, only 34 hits. Frederic arrived second, and retreated at once. Forgot the number of hits, no battle either. Then there was a battle in Dresden, Frederic and column against the whole Austrian army. Prussia lost, and part of the Austrian army (one column) ended up in Dresden. The other column and their army stayed in Pirna.
After that the column from the east arrived in Pirna, and fought the whole Austrian army (and lost).
It seems the Austrians pulled of what I tried earlier: getting the whole army to fight the enemy, when advancing one column to the region, and keeping the army and the other columns one region back. Only my troops refuse to engage - not only when a region back, but even when sended in together. And this isnt the first time this game either, tried it twice before, with the same result, the leading column takes one look, and goes home. (Squarian ran on eof these turns a second time, then they engaged as intended, and won handily).
Oh, and after loosing the battle both the army (under Frederic) and the column ended up retreating across the river. As the (attempted) battle was in Pirna, and then in Dresden (where part of my troops retreated to and Squarian was headed), crossing the river after that was rather unexpected - retreatng along the river was more logical. Now I have to gather my army together again, travel north, and cross the river, before I am positioned between the Austrians and Berlin. If they also move north they can outmarch me easily.

.
I noticed this behaviour (the preference to crossing rivers or larger bodies of water when retreating) in WIA, with Whasinghton (the master of retreat - he actually retreated quite often after having won a battle). But at least with hime we could think it historical (he retreated across the Delaware several times in our game).