UserType and tiny blob

Hi,
I have a domain object defined as follow :

class Question {

    String name
    String description
    LinkedHashMap<String,AbstractParameter> params = new LinkedHashMap<String,AbstractParameter>(20)




    static embedded = ['params']

    static mapping = { params type: LinkedHashMapUserType }

    static constraints={
        params(maxSize:1048567)
    }

 
}

To store the "params" attribute, I have my own hibernate  UserType.

By setting the maxSize constraint, I expect the blob size of the "params" column  to be Medium, but it remains Tiny...

So does the constraint mechanism drives the blob size in this case  ?

Regards,

Olivier.