Thank you very much for your reply.
I am very sorry, but this is limited to 30. Every time you refresh or open Stock Central, the system has to recalculate through tons of data. If we had to allow larger limit sites may hang or worse.
WooCommerce is already working on a new system that should speed up everything. If we find it good enough, we will increase the limit next year.
You can use the WC report instead.
Hope this helps.