I always do this with vocals that are a bit unruly and it's a great way of making the compression sound a lot less obvious without losing evenness. Also, when you get really bad plosives (P's, T's and F's) that trigger unwanted compression, you can automate a highpass filter to remove everything up to 350hz. On paper it sounds extreme but, if you do it only on those problematic spots, it makes everything sound much more professional.
Maybe you're using the wrong compressor type for this application? The LA2A being an optical circuit is of course going to react more slowly, what happens if you use a lightning fast compressor like an 1176 instead?
I think the 1176 by itself would make the compression even more obvious since it would react so fast to the changes in level. Evening out the vocal with clip gain should help no matter what compressor you choose.
