I use webproxy but why my connection becomes slower and not responsive?

This often happens, we mean to use a web proxy to make browsing so much faster because of content that had previously accessed does not need to be taken again from the internet. But, in fact the connection is even be slower and not responsive. So often arise a question to myself "why even slow if I use webproxy". You know, where lies the fault?
The answer in my experience is a masquerade NAT is more than one. First check the topology of the web proxy in your network, if aligned with the client use a proxy address list. Configuration such as this

/ip fi address-list ad address=(ip-proxy-anda) list=proxy
/ip fi nat ad chain=dstnat in-interface=(ethernet-LAN) to-address=(ip-proxy-anda) to-port=3128 src-address-list=!proxy comment="redirect-proxy"

  The next step will disable all NAT masquerade except to the public interface (internet) and NAT with the comment "redirect-proxy"
Then position the masquerade NAT public interface is at the top.
Then try browsing through the results with tests pc client. Hopefully success.