In my experience, it is very tricky to get solid recognition on single-syllable words like "lock" or "zoom" or "deck" especially if they involve a harsh staticy "ck" sound. This is probably because the speech recognizer is designed to work well with phrases, sentences, and optimized for natural language as if you are dictating into a word processor. SAPI is also designed for low quality PC mics and aggressively filters out what it considers noise. You can adjust this stuff via Control Panel but you either get accurate but rarer recognition (you repeat commands often), or get frequent but inaccurate recognition where it's making it's best guess and making mistakes. The sliders in Control Panel help this a bit and have to be very carefully tuned for each setup.
It is more likely to understand "lock the target" versus "lock target" and both of those are much better than "lock" simply because it is multiple words that are spoken in sequence, and it looks at the entire phrase as a group entity and analyzes how english speakers tend to chain words together to assist recognition. The more you say, the more likely it is to get it right.
I also noticed that random room noise, noise from the game (5.1 surround sound here LOL) and keyboard clicks would often result in "lock" or "zoom" being falsely detected. I found that I really couldn't get decent recognition with these until I bought a very high quality mic and spent a lot of time tuning it. I ended up changing a lot of phrases so that they would be 1.) Sufficiently different from all other phrases and 2.) Sufficiently complex to help recognition without being overly wordy. It's an art, for sure.
The most important things are to 1.) Practice and establish your speaking style as it will be used in-game, 2.) Adjust the mic volumes via the speech control panel so they are perfect for your style/mic distance/room noise/etc, 3.) Then go through as many of the speech training wizards as you can, then 4.) Adjust the sliders in speech control panel to fine tune as room conditions, mic distance, and laryngitis dictate.