Its present in many AGE titles, in effect where the warfare took place with armies with a relatively well structured command structure and decent roads/communications. Its absent from AJE (where in truth the scope for cross country movement is limited) and WiA (where I have always assumed that this reflects the low density of troops and the poor communications).
In Rise of Prussia its subject to some debate with some players deeming it too 'Napoleonic'. I personally think that is based on a misunderstanding of what is being simulated. Its also been a subject of debate in ACW2 and EAW, not least in where the forces end up after the battle.
So what appears to happen is if a battle occurs and if separate corps of the same army are in adjacent provinces, those other units can appear on the battlefield after the first hour and may contribute in future combat rounds (or drop out). In effect it looks like a pre-mechanised force moves x kms to battle in an hour (this is the RoP complaint). In different iterations of the AGE engine, units that marched either then return to their original province or end up in the battle province - either as victors or retreating.
What it represents to me is something slightly different. A problem with WEGO is how to model response to enemy moves and this is one reason why WEGO is rarely used in operational/strategic games with large numbers of motorised formations.
My interpretation of MTSG is there is a lot of low level screening/scouting/intelligence gathering going on below the level of player involvement. This has the chance to detect an enemy move and in turn trigger a response based on initiative. If that is triggered then the supporting units move to where a battle is to be fought. The criteria model inactivity, distance, military control and ease of march into the formula, meaning a response is more likely with active commanders linked by a road net and relatively unlikely if a battle happens on the other side of a major river (unless there is a bridge). Key is that the response modelled by MTSG starts not with the moment of combat commencing but in the period beforehand when its clear that something is happening.
This is probably completely obvious to many players but I've had to spend some time thinking over this mechanism - not least, as above, its a regular issue in RoP. Also it seems at first sight rather unintuitive, but its clearly a significant feature in the entire AGEOD approach to combat modelling.
You can of course remove it from a game, or reduce all the chances above. For most games its in the text file gamelogic as:
resBaseChanceDef = 90 // Base chance if in Defensive posture
resCostPerDay = 10 // -10% for each day of marching
resCohCostPerDay = -1 // -1 cohesion for each day of marching
resModAdjGHQ = 10 // +10% if adjacent to army HQ
resModIsGHQ = 25 // +25% if the army HQ itself
resModLeaderStrat = 5 // +5% for each pt of strat factor of the leader
resControlChunkMod = 5 // Every 5% of MC lacking gives -1% chance (both for start and end region)
all you need to do is to set "resCostPerDay = 10" to 100 and the others to 0 and that will eliminate it.
Final bit, should the units return to where they came from?
There maybe good gameplay reasons for doing so, but in the context of battle for the era up to say 1900 I think they should. Its only at that stage that the concept of effective intervention via indirect fire, or of a battle front stretching 30+miles, becomes feasible. From a realist perspective in the context of the ACW timeframe I think they should all end up on the final battlefield.
