Changing input firing rate without changing orifice size

I have a 2014 Trio P3/Carlin EZ NGas boiler. With the welded flange (not universal) version and factory drilled .189” orifice it should fire at 85k BTU/hr. At installation it only clocked at 76k. DHW production via an indirect tank was marginal so I asked them if they could get it up to spec. They made a change and it actually went down to 68k. They did not change the orifice (I was there). What could they have changed to make it drop? What can be done to increase it?
Thanks very much