without knowing much about your environment, I would say you either need to rotate indices quicker (not a great solution) or use more indices to handle the inputs.
upping the total field size is a bad idea not just from a performance perspective, but if you keep adding sources, you could eventually hit that cap too.
The last suggestion would be to see if there is any normalization you can do. Do you have a schema? do you have/need src_ip, source_ip, SrcIP, ip_source, etc… or can you normalize it to only use source_ip?