HTTP/2 vs HTTP/1: no difference in download speed

First of all, I have just started to test Caddy and I am very pleased with its ease to configure. Well done.

I wanted to test the speed difference between HTTP/1 and HTTP/2 and for that purpose, I created a html file with about 100 pictures of about 150 K each. I was expecting a speed increase with HTTP/2 as all requests are sent simultaneously compared at maximum 6 at a time with HTTP/1. At least this is my understanding of one of the key features of H2.

Results in developer console (FF and Chrome, caching disabled) are a bit puzzling. Requests are sent synchronously as expected in H2 but the content download time are way higher than with H1. About 10 times slower, resulting in a similar total load time for H1 and H2 for the whole page. My Caddyfile is pretty standard and very basic (v0.10.10)

Results (download time in green)
HTTP∕1
HTTP∕2

Caddy file used for the test:

example.com {
 	root /var/www
}

caddy server is launched as a systemd service with:
caddy -log stdout -agree=true -conf=/etc/caddy/Caddyfile -root=/var/tmp

Any thoughts?

edit:

FF and Chrome seem to handle H2 differently , but the final download time are similar. Here is an extract from HAR file from FF and Chrome for the same url:

FF

   "timings": {
      "blocked": 0,
      "dns": 0,
      "connect": 0,
      "send": 0,
      "wait": 40,
      "receive": 1217
    }

Chrome

   "timings": {
      "blocked": 12.921664999001198,
      "dns": -1,
      "ssl": -1,
      "connect": -1,
      "send": 1.1470000008557992,
      "wait": 1105.3009999995993,
      "receive": 37.61300000041956,
      "_blocked_queueing": 7.665000000997679
    }

You might want to use webpagetest.org to rule out your local PC side factors and also enable video check box in webpagetest.org so you can check filmstrip as well to check first meaningful paint and speedindex times which is generally where HTTP/2 beats HTTP/1.1.

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