It might go down again on the Immigration Officer.. Maybe if IO is doubting the commitment of the relationship of the applicant, paying the RPRF upfront might mean a big deal... Still case to case basis and we don't know on what our applications will fall into..
In my case, I'm the applicant and I use my own credit card to pay the application fees.. Then on my FOSS notes, the IO put an entry that I'm the one who paid the application fees which should be the responsibility of the Sponsor.. For me it's not a problem coz in fact my credit card is just secondary of my coomon-law but the IO do not know that.. So as a damage control, I let my common-law use his credit card to pay my RPRF.....