Part of their formula is snap % and snaps played. It looks like that is hurting Willis in their projection, but that is because the snap % they are using is retrospective.
The actual pick awarded, IIRC, is based on snaps and snap % the season after they sign, which is how GB might get a comp pick for Eric Wilson and Josh Myers. Neither of their contracts signed would have netted them a comp pick, but because they both played such a high % of snaps last season, it boosted their points total to likely in the top 32 and thus the projected comp pick for both of them.
Assuming Willis is the starter and gets 90% of snaps (he got 12% of snaps last year with Love's injuries), I wouldn't bet on that being a 4th round pick just yet.