Tell them what you want to make. If the press, just say that your current role isn't directly related to the new one so that it doesn't make sense to compare. If they still press then just lie I guess. Or don't use recruiters.
Tell them what you want to make, and I agree with you that you call out that this role is different so the compensation isn't relevant.
Recruiters really are a terrible way to get a job. I've never gotten a job I liked or what I thought was a fair salary when I've used a recruiter.
Recruiters, used car salesmen, and telemarketers: if they were better people, they'd have better jobs.