Converting video int Webm using ffmpeg, file size

Question

I have found this article from google describing how to convert video into webm https://sites.google.com/a/webmproject.org/wiki/ffmpeg/vp9-encoding-guide

I used following command to convert video into webm.

1 Pass.

ffmpeg -i original/episode_19.mp4 -an -ss 00:02:23 -to 00:02:36 -c:v libvpx-vp9 -pass 1 -b:v 1000K -vf scale=-1:360 -threads 1 -speed 4 -tile-columns 0 -frame-parallel 0 -auto-alt-ref 1 -lag-in-frames 25 -g 9999 -aq-mode 0 -an -f webm /dev/null

2 Pass.

ffmpeg -i original/episode_19.mp4 -an -ss 00:02:23 -to 00:02:36 -c:v libvpx-vp9 -pass 2 -b:v 1000K -vf scale=-1:360 -threads 1 -speed 0 -tile-columns 0 -frame-parallel 0 -auto-alt-ref 1 -lag-in-frames 25 -g 9999 -aq-mode 0 -c:a libopus -b:a 64k -f webm converted/episode_19.webm

It produces great quality video. But the size of the file is not small enough to use it for web. In my case 12 sec video - 1.6mb. Interesting thing is that smaller resolutions results in a larger file. -vf scale=-1:360 without this argument video - 1.4mb.

My questions.

1. How to make file size as small as possible, but keeping quality good for web.
2. Why the converted video file size with smaller resolution is larger that original one

I would be grateful for any help.