I have just reviewed the pointer details ( re moving the Reinforcements "Flag" ).

It is first and foremost a standardish pointer with a few extra "bits". The actual pointer is smaller than normal, and has four Yellow marks above it ( two on each side ), in a design which is the same as the "in battle" command cursor. It also has a small red arrow to the left of the main pointer and below the left hand side Yellow marks. Is this what you have ?

You can indeed place the Flag anywhere on the map ! I suspect therefore, that it is possible to place it inside the "Red Zone" I referred to before - this IMHO may result in units not being able to enter the map ( but I may be wrong )... IMHO you should always avoid placing it too close to the Maps edge ( particularly if it is out of sight of your initial position ).

You say the Reinforcements button is Coloured ( as it should be ) ; however, do you also have the Green writing on the left hand side of the Battle Map ( just above the Unit Information Panels ) ?

[ This gives some information regarding the current standing of your Reinforcements ; listing the total number of units available, the number of units "mustering" towards the "Flag" and the number of units awaiting orders at the "Flag" ( or words to that effect ). By the way, does this list the correct total number of your Reinforcements ? ]

If these items are as they should be and you indeed have less than 16 units on the battlefield, then the first reinforcement units Unit Panel should appear as soon as you click on the reinforcements button. You are clicking on the correct button I presume ? i.e. the one that is on the left of the pair that are on the Top Right ( slightly away from the other top line buttons ) ?

[ Also note that as you appear to be placing the Flag towards the centre of the Map, the Reinforcement unit/s will take a long time to get there... ]