Yeast Pitching Rates

Can someone please explain to me about yeast. I tried to make high abv beer and used alot of malt, but only 1 pack of yeast. If I let the beer sit longer will it eventually all ferment? or do you have to use more yeast to get it to ferment?

Also when using a dry yeast and it says that it leaves low sediment is this because it doesn't ferment as well?

You should use more yeast for a big beer. Letting it sit longer doesn't necessarily bring more fermentation, as the yeast only has so much to give. You an google the Mr Malty calculator for amounts.

Some yeast are more flocculent than others, that is, they fall to the bottom of the fermenter. It doesn't mean they ferment poorly. Flocculation is just another characteristic of yeast. No idea why some do it better than others.