REFERENCE PLANE WALLS AND COLUMNS ARE DRAWN ABOVE AND BELOW

[amghma]

Dear all,

I am defining a reference plane to define the mezzanine story, but I have faced some issues :

1- the columns and walls drawn are drawn above and below the reference plane as one unit,I cant delete the upper part, how can I have it below a reference plan only ?
2- I cant import arch layer to a reference plan, is there is another option to do so ?

looking for your opinions