Aliens tend to select low-TU firemodes for reaction fire, which is why they seem to RF a lot. If you want to increase the amount of RF your soldiers take, be sure you are using low-TU firemodes as your RF firemode. It's easy to miss, but you can select the RF mode by clicking a small circle in the bottom left of the firemode panel.
Also keep in mind that if a unit loses sight of another unit at any time, the TU accumulation must start again from zero. In 2.5-dev, at least, I find aliens are good at walking behind you before firing, so in tight spaces I'll often try to form a line to block their movement.