Well large field mtt ROI can fluctuate widely of/c. Just holding near even can be acceptable while waiting for that big win, and if/when you get it your ROI can be astronomical.
This is what happened to me. I was just about even, maybe slightly negative, before my 1st place win in a FT $25K Guarantee, which shot me to like 1100% ROI, LOL. I'm still around 900% since then but obviously can't maintain those ridiculous numbers. I've actually played in very few large MTTs since, though, but have been doing pretty well in multi-table SnG's, with a little better than 22% ITM rate currently. Honestly I don't pay that much attention to my ROI because of the fluke spike, but I do watch my ITM% pretty closely.
EDIT: Just looking up my FT stats on OPR, they have me as 1482% ROI for the year but only 18% ITM. HEM has me at about 900% and 22.4% ITM, but HEM is figuring in all sites and not just FT. I'd need to filter on FT to see how they really compare. Speaking of, is there a way to aggregate numbers across
poker sites on any of the online stats sites?