Нет, с размером там всё в порядке, 100м стоит. Загружаемые файлы значительно меньше.
P.S. в форме ранее пропущено - enctype="multipart/form-data"

myserver.conf
-------------------

server {
listen 80;
server_name myserver.ru www.myserver.ru;
return 301 https://myserver.ru$request_uri;
}

server {
listen 443 ssl http2;
server_name myserver.ru;

access_log /var/log/nginx/myserver.ru.access.log main;
error_log /var/log/nginx/myserver.ru.error.log debug;

location '/.well-known/acme-challenge' {
default_type "text/plain";
root /tmp/letsencrypt-auto;
}

ssl on;

ssl_session_cache shared:SSL:2m;

ssl_stapling on;
ssl_stapling_verify on;

resolver_timeout 10s;

ssl_certificate /etc/letsencrypt/live/myserver.ru/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/myserver.ru/privkey.pem;

include /etc/letsencrypt/options-ssl-nginx.conf;

ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem;

root /var/www/html/myserver.ru/;

index index.php;

charset utf-8;

location / {
root /var/www/html/myserver.ru;
if (!-e $request_filename) {
rewrite ^/(.*)$ /index.php?$1 last;
}
}

location /rulers/ {
root /var/www/html/myserver.ru;
if (!-e $request_filename) {
rewrite ^/(.*)$ /index.php?action=manager&$1 last;
}
}

location /api {
root /var/www/html/myserver.ru;
if (!-e $request_filename) {
rewrite ^/(.*)$ /sttapi.php?$1 last;
}
}

location /api2 {
try_files $uri $uri/ /sttapi.php;
}

location ~ \.php$ {
root /var/www/html/myserver.ru/;

fastcgi_pass unix:/var/run/php-fpm/myserver.ru.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;
}

}


nginx.conf
--------------
user nginx;

worker_processes auto;

error_log /var/log/nginx/error.log;

pid /run/nginx.pid;

include /usr/share/nginx/modules/*.conf;

events {
worker_connections 1024;
}

http {

log_format main '$remote_addr - $remote_user [$time_local] "$request" '
'$status $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for"';

access_log /var/log/nginx/access.log main;

sendfile on;

tcp_nopush on;
tcp_nodelay on;

keepalive_timeout 65;
send_timeout 60;

types_hash_max_size 2048;

client_max_body_size 100m;

index index.php index.html;

default_type application/octet-stream;

gzip on;
gzip_disable "msie6";
gzip_vary on;
gzip_proxied any;
gzip_comp_level 6;
gzip_buffers 16 8k;
gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml appliction/xml+rss text/javascript;

include /etc/nginx/conf.d/*.conf;
include /etc/nginx/mime.types;

}