RLH (root likelihood) depends strongly on the number of concepts shown in each task. If just 2 concepts are shown, then the chance RLH rate is 0.5. With 10 concepts per task, the chance RLH rate is 0.1. So, you cannot compare RLH between studies unless you somehow adjust for number of concepts shown per task. Pct. Crt. does that. It can be treated like a pseudo-Rsquared.
In a recent training, I reported Pct.Cert results for HB estimation for 25 commercial and methodological CBC studies (standard first-choice CBCs...not DRNone, chip allocation, or B-W responses). I had a mean Pct. Cert across those studies of 0.71, with a min of 0.60 and a max of 0.83.
So, you want to be in that range.