Using Sugar in Bottles/Kegs.

Allo.
I've been using BeerSmith for the last year or so, but mainly been bottle conditioning my beers and so chosen Table sugar/Bottle as carbonation method.
Recently I've come over a "couple" of keg's which I thought I'd use to carbonate in, use clear draught and fill bottles.
Problem for me is that when I choose keg with table sugar, it says it requires about half the amount then in Bottles? 
Second problem is that I will still get a couple of bottles to fill even when using keg's.

So,, how should I treat this?
Go for only using Table sugar / Bottle or Keg with table sugar?

Ah, and if someone could explain why it only needs half the sugar in keg's I'd be happy

When you carbonate in a keg using priming sugar you'll still need a propellant, in this case CO2, for dispensing. Without a constant pressure applied the pressure in your keg will decrease, incrementally, with every bottle you fill. As pressure drops, CO2 will come out of solution and the carbonation level of each bottle will be slightly less than the previous one, until you're left with very little carbonation at some point, and likely not enough pressure to dispense the remaining beer. Assuming you don't have the ability to chill a keg of beer, you'll also likely have a problem with excessive foaming when filling bottles.

A set amount of priming sugar will produce a set amount of CO2 when metabolized by the yeast. When fully carbonated, your beer will have reached equilibrium, a point where the beer won't absorb any more CO2. A larger volume of head space will require more CO2 to reach a set pressure.  Approximately 53, 12 oz. bottles (5 gallons) have more combined head space than a Corny keg filled with the same 5 gallons of beer, so will need more CO2 to achieve the same carbonation level. Because gasses compress much more readily than liquids, the amount of additional CO2 needed to achieve the same carbonation level in the bottles will be considerable more than the volumetric difference.

Thanks 
I should have thought of that.
The previous batches I've as I said, gone by the sugar/bottle table, and I racked one with the lower ratio in yesterday, and one with my normal ratio.

Transferring to bottles haven't been a foaming issue for me, bought a counterfiller from Ali site a while ago and found a video showing how to use it.
The way they described it, and how I'm currently doing, is to have a quick connect carbonation cap in a armed tube, a t-cross and tubes going both to the keg and the counterfiller.
I normally keep the keg at around 40F, and have had no issues with foam  8)

The type counterfiller I use:
https://www.morebeer.com/products/counter-pressure-bottle-filler.html