Emperor, just a thought, if you made certain weapons that currently have direct and indirect fire as options several things would have to happen, as I see it.
1. The points cost for the weapon losing indirect fire mode would need to be altered or reduced, as the weapon is now less useful.
2 Unit would need specific options to be able to equip with an indirect mode weapon at some reduced cost to be determined.
3. Units which are forced to have to chose (direct or indirect weapon)would need to cost less as a unit, because they would be much less flexible tactically, or the unit would need to have the possible number of those weapons available altered to maintain that flexibility ie. add one more special weapon option (3 instead of two) or possibly both.
4. create a number of new weapons and miniatures to represent them so you would have a direct fire Javelin and an indirect fire Javelin equivalent.
5. Some have proposed going to a special deviation die and allowing the shot to deviate in any direction (bad IMHO) this actually relects artillery usage pre Napoleonic Era as modern prectice is fire spotting shots call over under correct fire, then Fire for effect. Actual deviation in modern Artillery does tend to be euther long, short or on target. Lateral deviation is most commonly the Battery Officer making a mistake.
With the current system simply learn to do the Arithmetic as cited in the book and forget the chart. The chart will confuse you.
I haven't even looked for a while but Odds long, select point of impact each odd die thrown adds that many inches 5 (5") each even subtracts 6 (-6") total in example -1" toward firer.
Odd Short, odd numbers subtract, even numbers add (5,6) 1 inch long.
Odd Long, odd numbers add, even numbers subtract (5,6) 1 inch short.
Even Long, even numbers add, odd subtract (6,5) plus 1 inch.
Even short, even numbers subtract, odd add (6,5) minus 1 inch.
Doubles "always" HIT.
Should take most players five to ten minutes doing a few calculations to be able to forget that confusing table.
I just worked it out while writing this message. It is not a difficult concept.
If anyone is having difficulty, draw out a number line from -11 to +11 and chart a few dice throws on it. To give you confidence in your arithmetic look up the first dozen calculations on the chart to verify your results.
As for not allowing indirect fire weapons to fire direct and hit, try boresighting a 155 Howitzer on a target too close to hit easily with indirect fire. A Beehive round at 150 to 300 meters is devastating and accurate. By the way that is why many artillery pieces bother to have actual sights on them. All indirect fire is done off Artillery Fire Tables with fire and correct.
Basically all of the above states my position for saying I think the current system works pretty well for a Game. Therefore it actually does not need to be tweaked or modified.