As per this Fallout 4 Perks Comparison Guide:
Combat Medic (heal 100 points if health falls below 10%; can only be used once each day)
This says to me that in the instance your health drops below 10% then you will gain 100 hit points up to a maximum of one time per day.
The other answers supplied were very helpful, but didn't state the best solution which, in the words of Charlie Sheen, is
"Drugs."
Agility points help flight and action points help duration.
Per all my testing the height appears to be capped. (At approx 20 meters; using very rough vertical measurement by setting POV in fixed position and using reference features on buildings, etc.)
The total ground you can cover, however, depends on thrust management.
I was able to fly from the big island in bottom right corner of map (the one you can occupy, forgot the name) to the shore (near the old refinery/dung farm which looks like shortest island-mainland distance). It's been a while since I played FO4, so going from memory for now..
Here is how I get super long (but not high) flights with power armor jetpack:
- Max natural agility (perks + bobblehead)
- Agility paintjob on armor
- Food items that grant bonuses to AGI and AP (deathclaw steak, mole rat chunks, cooked softshell meat, and maybe a couple others, I think.)
- Drugs that grant bonuses to AGI and AP (usually carry x100 jetfuel and hotkey it.. constantly addicted to Jet :D )
- Maxed Perks that increase power armor efficiency and movement speed (Though I have not yet confirmed that this has any effect; just stating that I had these before even crafting the jetpack; need to test with different unbuffed char next)
- Hotkey Ultrajet (although Jet works pretty good too since you can quickly regain the "high" with hotkeys)
- Make a running jump, and use Jet as you are running or jumping.
- Focus on distance, not height. The trick is to manage thrust carefully, tapping jump key only as needed, NOT holding it down. This is sorta possible without jet, but much easier while time is slowed. If you run out of jet, take some more! (Yeah, you'll get addicted, but don't worry! Addiction is a joke in this game compared to the previous ones; 4 diff ways to cure it. Or get perk where you never get addicted to chems.)
Also note that Jetpack + Quad-barrel Missile Launcher + Jet = Archangel of Death
Best Answer
This is hypothetical and based off info on the wiki, but I think focus relates to the amount of action points used.
If we look at the Laser Pistol table, in the Sights section, we can see that both sights having a bonus to "focus" also decrease the action points cost while all other sights cause an increase:
If we take a detailed look at the Improved sights, which claims to have an increase in 'focus and sighted accuracy', we can see that the only attribute changed is the accuracy, plus the AP cost from the previous table:
Since the only two attributes changed are the accuracy and AP cost, and the weapon claims to change the accuracy and focus, we can deduce that focus is the AP cost.