Frontend subfolder to backend root

Hello i have a problem with understanding whats wrong.

I want on the frontend come with a subfolder

frontend port_80
bind *:80
mode http
acl host1_path path_beg /host1
use_backend host1 if host1_path

backend host1
mode http
reqrep ^([^\ ]\ /)host1[/]?(.) \1\2
server host1
errorfile 503 /etc/haproxy/errors/503.http

The webside load not correct. Whe i try without subfolder on the front, the webseide load. How can a make at frontside match on subfolder and the backend stay in the root from the backend server?

on final i will make 3-4 more subfolder redirect to another server.