Here is a cascade noise figure calculator. Play around with different gain figures and noise figures for the first amp to see how it affects the total noise figure. Consider the second amp your receiver. Put in an 8 db or so figure for the second amp to simulate your receiver.
You will see that as you increase the first amp gain the overall noise figure does drop some but not by as much as the gain increase. You can simulate a pad between the preamp and your receiver by increasing the noise figure of the second amp by the amount of pad you would use. It is not quit the same as reducing the gain of the preamp (first amp) but close. http://www.minicircuits.com/pages/mcl_nf_calc.html 73 Gary K4FMX
