problem with tables in RevTex 4 class

I am using Revtex 4 class but I have a problem with the alignment of the text in the table.

Here is my code, is there any way to center align all data with wrapping text if needed?

Note: it looks good in the article class…

Thank you.

documentclass[fleqn,12pt,floatfix,superscriptaddress]{revtex4}
usepackage{amsfonts}
usepackage{amsmath} 
usepackage{amssymb}
 usepackage{tabularx,ragged2e,booktabs}
 newcolumntype{C}{>{Centeringarraybackslash}X}
    usepackage{multirow} 
begin{document}
begin{table}
caption{Parameters}
begin{tabularx}{textwidth}{@{}ccccCC@{}}
hline
Altitude & $alpha$  &  $bar{H}$ &  
$bar{o} $ & velocity $lambda$ with streaming &  velocity 
$lambda$ without streaming
hline 
 400 km  & 7  & 6  & 1  & 2 & 1
 500 km  & 5  & 6  & 5  & 3 & 1 
 600 km  & 29 & 8  & 55 & 4 & 2 
 700 km  & 6  & 10 & 6  & 4 & 2
 800 km  & 4  & 13 & 8  & 4 & 2
 900 km  & 2  & 14 & 4  & 4 & 2
 1000 km & 5  & 14 & 4  & 5 & 2
 hline
end{tabularx}
label{table:1}
 end{table}
  end{document}