Rallying over the radio is not as effective as doing so with the personal touch.

Imaginary radio conversation to illustrate the point.... an attempt by Lieutenant Notsobright of the Last Chance Militia trying to rally Sergeant Survivor and his Squad to counterattack an enemy position while they are instead busy departing the battlefield (with some haste)....

Red Dog Three, Red Dog Six. Halt in place. Reform and execute Opord Omega, Grid 57.
Translation: Attack the dug in enemy on the hill in bunkers with lots of machine guns.... after rallying your troops because I said so....

Red (zzzt-crackle) Six, (hiss-zzt) Dog Three. Not receiving (crackle) last... say (buzz-hiss).
Translation: Sgt. Survivor isn't an idiot, and doesn't plan to lead a suicide charge... especially with a broken unit that is busy trying to head for the nearest part of Nowhere it can find.... the eltee's rally attempt just isn't terribly motivating to the Sergeant and his battered squad who are legging it.... and of course, although his radio is receiving fine, the Sergeant is busy providing simulated static and squelch back to his CO to give the impression of poor reception....

Now, if Lt. Notsobright had been standing right beside Sgt. Survivor, the Sergeant would have had far fewer options to ignore him, hence making his rallying attempt much more likely to succeed.

When rallying troops, apply a 1 die-shift negative modifier to the quality die of the officer rallying the troops if he is not within 6" (face to face).