Napoleon was a lot more aware of the Prussians on the 17th/18th than history gives credit to and I know, this flies in the face of Coppens... in my book, there is a 20 page appendix that lists out all the evidence that the French had trickling in about the Prussians. (this appendix is written by Coppens favorite person, ha! But the evidence is as sound as any from 1815.)
However, it is absolutely true that Napoleon never realized the extent of the Prussian presence, and grossly underestimated it.
Regardless of whatever was discussed by the Allied command, I focus just on what Napoleon knew/was told/thought for my analysis of French operations. Napoleon himself said in exile that he might should have retreated (at assuming Waterloo) when he realized the superiority of the Prussians. (note, the quote is vague, and some interpret it to mean Ligny - which is very possible because Napoleon was surprised there too, and retreating would be consistent with the idea that the campaign was a political one, seize Brussels, and that he was not yet prepare to risk the cream of his army for a victory that would not change much - and even destroying the Prussians would not have changed the political calculus.)
I definitely believe (from the pre-printed proclamations to the correspondence) that Napoleon's primary goal was Brussels. In this particular instance at this particular time, he had a lot to gain on the home front from a political win, whereas normally his techniques worked best when he aimed at enemy army destruction. The idea that he would come between the allies and destroy each army in detail - I don't think Napoleon planned that because he clearly expected that once he gained a positional advantage, they would retreat.
And hence, I continue to complement Wellington and Blücher for their tenacity, and also point out that they (or Wellington) understood much the same as Napoleon did - that there were great gains for Napoleon in a victory in Belgium. The Allies were getting frequent detailed reports about the French interior (some written by Fouché) and they understood that Napoleon sat on a divided country, skeptical merchants, mixed enthusiasm with the recruiting, etc. A political success (that Napoleon would certainly overstate) could have greatly strengthened his hand.
The Napoleon of 1815, had he chosen a defensive campaign in France with an intact mobile army and with Davout in Paris with a large army and with sizable forces around the country - well, while most like to say Allies couldn't lose, my money would be on Napoleon........ except...... this is predicated that the army could function, and in Belgium, the staff work was a net-negative. Whether that was the intention or not, by the time we finish our story on June 18th, at least everyone will know exactly what Soult's failings were, rather than just the vague "he was a poor choice."
On the other hand, maybe Napoleon was doomed from the start, and Wellington only faced him south of Brussels for his WELLINGTON'S OWN PERSONAL GLORY! Bastard!