This is only my second time using trays. I quickly switched to tanks due to scratching when I first started 4x5". If I am doing a single sheet. I agitate once per minute. Last night I had three sheets so I was pulling the bottom sheet and draining it off per A.A. "The Negative." Accept I think he recommends a 30 second cycle, but I don't think that would halve the dev time. I feel like I am doing something wrong for it to be off by that much. I first suspected fogging, but I have ruled that out.
I am shooting to get them to print nice on normal polycontrast paper without a filter. This might require a little more punch than enlarging. I don't have a 5x7 enlarger or a scanner that can handle anything bigger than 4x5", so I have to contact print everything.