Hello,
I played with wms in the attachments on the left 4.8.2 on the right 4.8.2.1:
with the same configuration I was unable to display the same level on both.
http://serviziogc.regione.fvg.it/geoserver/ows?SERVICE=WMS&
I also think that a filter is needed for the levels in the case of this service they are really many and you have to scroll through the list to find the one you want.
On the page for selecting the wms services already available, a filter based on the current position would be required. Services not available for your area are useless.
I played with wms in the attachments on the left 4.8.2 on the right 4.8.2.1:
with the same configuration I was unable to display the same level on both.
http://serviziogc.regione.fvg.it/geoserver/ows?SERVICE=WMS&
I also think that a filter is needed for the levels in the case of this service they are really many and you have to scroll through the list to find the one you want.
On the page for selecting the wms services already available, a filter based on the current position would be required. Services not available for your area are useless.

. Your idea with possibility of overlay layer with opacity makes sense. We do not have it on our road map for next months. I would recommend / ask you for a favor to create idea on the help desk so others can vote for it and watch progress
.