Redtail Tiger catfish hybirds size?

Just wanted to know if anyone knows how big a Redtail cat and a Tiger Shovelnose catfish hybird gets? I have and had many Redtail and Tigers. I had a redtail that grew a little over 3 feet FAST. But I set up a new tank last year with 1 Redtail 1 Tiger and 1 hybird. Redtail and Tiger are both over 1 1/2 feet now and hybird is only 10 inches and they all were the same size when I got them. So any info? Thanks.