adding sugar to fermentor... does any just sink to the bottom and not ferment?

This might be a stupid question... but I have heard a lot of times if you do a big beer that you might want to add the sugar addition (for maybe a BIG dipa or tripel or something like that) into the fermentor 2-3 days into fermentation instead of the boil to make sure that it ferments out as much as possible. My question with this is, if I boil some sugar with a bit of water, make it into a syrup and then add it into the fermentor, the yeast will get that bit too, there won't be a propensity to just sink to the bottom and not ferment out will there?
Just wanted to make sure =)

THanks!

The yeast will find it.

But yes, you are correct. While yeast will find the sugar, like us they prefer the "low-hanging fruit." The sugar chains from malt are likely slightly longer than simple sugars you will add later. This makes them just a little harder to ferment. If you add them all together, the yeast will eat the simpler sugars faster than the other (usually fermentable) sugars. So you may not attenuate out completely. This issue can be mitigated by making the yeast do the hard work first and the easier work second. This only occurs if you approach the alcohol tolerance of the yeast.

I think.

Correct me if I am wrong.

That is what I would have thought but I wanted to make sure! Anyone else weigh in as that's what happens?