Hi,
The hallmakrs clearly identify a 800/1000 silver monstrance made in Paris (not in Lyon) between 1819 and 1838. These hallmarks are punched according to the french regulations for what concern their location and their countermarking. So there is no doubt about this part of the identification.
It is a bit different for the maker identification. Firstly you should have a look at the following:
https://www.silvercollection.it/ASCASFAVIERING.html and more specifically the Favier family tree.
Despite the difficulty to read the maker's mark on the photos I think that there is no exact match with the same font. It is also strange that the mark with the full name FAVIER was entered in 1846 by Pierre-Henri Favier which is much later than the making date. Could it be another maker ?
Hope it helps.
Dinio