[Avodah] One size fits all?

[I. Balbin]

I am being a little lazy here. I could look in various Tshuvos,  
including Bnei Banim etc
At a wedding, IF it is decided that there will be a Mechitza then I  
would expect that there ought to be two dinim/hanhogos
therein. For the "dance floor" one would expect a Mechitza that was  
dense enough and high enough to prevent
Histaklus, as per one loshen of the Rambam, with the aim being to  
prevent men being able to see women
dancing. What about the other component, where people are sitting. Is  
there an Inyan of Histaklus here as well
because presumably the main reason is a) Shesimcha BIMONO b) prevent  
Hisarvus
Yes, I am aware of Deyos that say say you don't need one etc, and I am  
not at all saying that you do.
Rather, I am asking, according to those who say that you do need one  
for this component, is the Mehus of the
Mechitzah requirement different for those two sections of a hall  
(assume all are seated in one hall)
Would, for example, there be able to be gaps of a maximum size between  
(say) pot plants, and would the height of those
pot plants be able to be theoretically lower than the dance floor  
section.

I have noticed that when it comes to "finger food" or "smorgasbord"  
prior to the Seuda proper, people who do have
a Mechitza seemingly rely on no Mechitza and/or men/women being on  
either side of a room. Is that a din of Hisarvus (mixing) that they  
are "meikel" on (because inside the room they do have a Mechitza)