About reaction fire - it doesn't always work, and even though I double "tick" the reaction fire button, and some TUs get wasted for that, after I spend all of my remaining TUs for movement, inventory, etc, the actor doesn't use the RF if an alien gets close.
I have a suggestion: how about normal reaction fire (one check) to make the soldier use all the saved TUs for RF and the ones left from the previous turn for taking one or several shots (if enough TUs) using the primary fire mode of the weapon, and for double checked RF to use the secondary, more powerfull mode, of the weapon?
Besides, you could make a smarter RF mode, preventing the soldier to use all the TUs for shoting an alien twice if just one will be enough to kill it. Thus, the soldier can use RF multiple times in a turn, if has enough TUs for several shots. Some weapons, like pistols, require less TUs.