Not that it may also be that the alien has to spend the TU within your soldier's RF range. Your soldiers won't RF out to the full range of their weapons, they only shoot if the %hit chance is over about 40% or so. Or perhaps it's a range based on the range of the weapon, I've certainly seen flamer equipped soldiers not RF (candlelight, 8 TUs) aliens within their range who moved into view and shot them with plasma rifles.
It also seems that an alien breaking LOS/line-of-fire at any time for any reason may reset the RF/TU count. I haven't experimented to see if switching soldiers and acting with a second soldier before returning to the first soldier can reset alien RF/TU counts.
RF is an area that has a big "Needs testing" sign hung on it.