I agree with most of what you said, apart from the last paragraph. In a real life war like WW2 or WW1, (idk about modern because guerilla tactics are commonly used in the years 1950 and above.) If you have a massive gap in your line, the enemy can go behind and flank you, this was the case in the 1st Battle of Marne, where a gap was opened up in the German lines, forcing the Germans to retreat. Another scenario is the encirclement at Dunkirk, as Wehrmacht troops punched through the undefended Ardennes which caused on a major defeat for the Allies. If you lose a battle which like a gap is opened up, you can use the troops in the side of the gap to push through, and just fill the remaining with like 1000 or so troops, and the enemies who tried to break the line are now encircled. And what I like to do to prevent that is to station troops behind your frontlines, like 300 or so troops, to prevent that, as I assume unless youre fighting a major power, would've taken massive casualties, and you reserve troops could just kill them and fix the lines.