How to add boost during (before) indexing a couched using elastic search

Hi all, based on some posts, I did the following:

curl -XPUT http://localhost:9200/testdb/testdb/_mapping -d '{"myObj":{"prop1":{"boost":"25.0","include_in_all":"true"}}}'

and then did the indexing again:

curl -XPUT 'http://localhost:9200/_river/testdb/_meta' -d '{
"type" : "couchdb",
"couchdb" : {
"host" : "localhost",
"port" : 5984,
"db" : "testdb",
"filter" : null
},
"index" : {
"index" : "testdb",
"type" : "testdb",
"bulk_size" : "100",
"bulk_timeout" : "10ms"
}
}'

but still I don't see any changes in results pre/post boosting. I did a strong "25" boost, just so that I can see some changes to make sure that this way of boosting at index time works...
I read a few posts where people have done it, but can't seem to reproduce.

Can anyone tell me what I'm doing wrong, or tell me how to do the boosting at the time of indexing?

Thanks!